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![Gautham R. Shenoy](/assets/img/avatar_default.png)
We are currently assuming that CEDE(0) has exit latency 10us, since there is no way for us to query from the platform. However, if the wakeup latency of an Extended CEDE state is smaller than 10us, then we can be sure that the exit latency of CEDE(0) cannot be more than that. In this patch, we fix the exit latency of CEDE(0) if we discover an Extended CEDE state with wakeup latency smaller than 10us. Benchmark results: On POWER8, this patch does not have any impact since the advertized latency of Extended CEDE (1) is 30us which is higher than the default latency of CEDE (0) which is 10us. On POWER9 we see improvement the single-threaded performance of ebizzy, and no regression in the wakeup latency or the number of context-switches. ebizzy: 2 ebizzy threads bound to the same big-core. 25% improvement in the avg records/s with patch. x without_patch * with_patch N Min Max Median Avg Stddev x 10 2491089 5834307 5398375 4244335 1596244.9 * 10 2893813 5834474 5832448 5327281.3 1055941.4 context_switch2: There is no major regression observed with this patch as seen from the context_switch2 benchmark. context_switch2 across CPU0 CPU1 (Both belong to same big-core, but different small cores). We observe a minor 0.14% regression in the number of context-switches (higher is better). x without_patch * with_patch N Min Max Median Avg Stddev x 500 348872 362236 354712 354745.69 2711.827 * 500 349422 361452 353942 354215.4 2576.9258 Difference at 99.0% confidence -530.288 +/- 430.963 -0.149484% +/- 0.121485% (Student's t, pooled s = 2645.24) context_switch2 across CPU0 CPU8 (Different big-cores). We observe a 0.37% improvement in the number of context-switches (higher is better). x without_patch * with_patch N Min Max Median Avg Stddev x 500 287956 294940 288896 288977.23 646.59295 * 500 288300 294646 289582 290064.76 1161.9992 Difference at 99.0% confidence 1087.53 +/- 153.194 0.376337% +/- 0.0530125% (Student's t, pooled s = 940.299) schbench: No major difference could be seen until the 99.9th percentile. Without-patch: Latency percentiles (usec) 50.0th: 29 75.0th: 39 90.0th: 49 95.0th: 59 *99.0th: 13104 99.5th: 14672 99.9th: 15824 min=0, max=17993 With-patch: Latency percentiles (usec) 50.0th: 29 75.0th: 40 90.0th: 50 95.0th: 61 *99.0th: 13648 99.5th: 14768 99.9th: 15664 min=0, max=29812 Signed-off-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com> [mpe: Minor formatting] Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/1596087177-30329-4-git-send-email-ego@linux.vnet.ibm.com
457 lines
12 KiB
C
457 lines
12 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* cpuidle-pseries - idle state cpuidle driver.
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* Adapted from drivers/idle/intel_idle.c and
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* drivers/acpi/processor_idle.c
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*
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*/
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/init.h>
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#include <linux/moduleparam.h>
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#include <linux/cpuidle.h>
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#include <linux/cpu.h>
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#include <linux/notifier.h>
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#include <asm/paca.h>
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#include <asm/reg.h>
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#include <asm/machdep.h>
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#include <asm/firmware.h>
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#include <asm/runlatch.h>
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#include <asm/idle.h>
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#include <asm/plpar_wrappers.h>
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#include <asm/rtas.h>
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static struct cpuidle_driver pseries_idle_driver = {
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.name = "pseries_idle",
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.owner = THIS_MODULE,
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};
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static int max_idle_state __read_mostly;
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static struct cpuidle_state *cpuidle_state_table __read_mostly;
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static u64 snooze_timeout __read_mostly;
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static bool snooze_timeout_en __read_mostly;
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static int snooze_loop(struct cpuidle_device *dev,
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struct cpuidle_driver *drv,
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int index)
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{
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u64 snooze_exit_time;
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set_thread_flag(TIF_POLLING_NRFLAG);
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pseries_idle_prolog();
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local_irq_enable();
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snooze_exit_time = get_tb() + snooze_timeout;
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while (!need_resched()) {
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HMT_low();
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HMT_very_low();
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if (likely(snooze_timeout_en) && get_tb() > snooze_exit_time) {
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/*
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* Task has not woken up but we are exiting the polling
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* loop anyway. Require a barrier after polling is
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* cleared to order subsequent test of need_resched().
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*/
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clear_thread_flag(TIF_POLLING_NRFLAG);
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smp_mb();
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break;
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}
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}
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HMT_medium();
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clear_thread_flag(TIF_POLLING_NRFLAG);
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local_irq_disable();
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pseries_idle_epilog();
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return index;
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}
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static void check_and_cede_processor(void)
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{
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/*
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* Ensure our interrupt state is properly tracked,
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* also checks if no interrupt has occurred while we
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* were soft-disabled
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*/
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if (prep_irq_for_idle()) {
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cede_processor();
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#ifdef CONFIG_TRACE_IRQFLAGS
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/* Ensure that H_CEDE returns with IRQs on */
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if (WARN_ON(!(mfmsr() & MSR_EE)))
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__hard_irq_enable();
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#endif
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}
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}
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/*
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* XCEDE: Extended CEDE states discovered through the
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* "ibm,get-systems-parameter" RTAS call with the token
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* CEDE_LATENCY_TOKEN
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*/
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/*
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* Section 7.3.16 System Parameters Option of PAPR version 2.8.1 has a
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* table with all the parameters to ibm,get-system-parameters.
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* CEDE_LATENCY_TOKEN corresponds to the token value for Cede Latency
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* Settings Information.
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*/
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#define CEDE_LATENCY_TOKEN 45
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/*
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* If the platform supports the cede latency settings information system
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* parameter it must provide the following information in the NULL terminated
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* parameter string:
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*
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* a. The first byte is the length “N” of each cede latency setting record minus
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* one (zero indicates a length of 1 byte).
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*
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* b. For each supported cede latency setting a cede latency setting record
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* consisting of the first “N” bytes as per the following table.
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*
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* -----------------------------
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* | Field | Field |
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* | Name | Length |
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* -----------------------------
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* | Cede Latency | 1 Byte |
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* | Specifier Value | |
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* -----------------------------
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* | Maximum wakeup | |
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* | latency in | 8 Bytes |
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* | tb-ticks | |
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* -----------------------------
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* | Responsive to | |
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* | external | 1 Byte |
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* | interrupts | |
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* -----------------------------
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*
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* This version has cede latency record size = 10.
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*
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* The structure xcede_latency_payload represents a) and b) with
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* xcede_latency_record representing the table in b).
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*
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* xcede_latency_parameter is what gets returned by
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* ibm,get-systems-parameter RTAS call when made with
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* CEDE_LATENCY_TOKEN.
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*
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* These structures are only used to represent the data obtained by the RTAS
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* call. The data is in big-endian.
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*/
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struct xcede_latency_record {
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u8 hint;
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__be64 latency_ticks;
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u8 wake_on_irqs;
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} __packed;
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// Make space for 16 records, which "should be enough".
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struct xcede_latency_payload {
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u8 record_size;
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struct xcede_latency_record records[16];
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} __packed;
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struct xcede_latency_parameter {
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__be16 payload_size;
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struct xcede_latency_payload payload;
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u8 null_char;
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} __packed;
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static unsigned int nr_xcede_records;
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static struct xcede_latency_parameter xcede_latency_parameter __initdata;
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static int __init parse_cede_parameters(void)
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{
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struct xcede_latency_payload *payload;
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u32 total_xcede_records_size;
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u8 xcede_record_size;
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u16 payload_size;
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int ret, i;
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ret = rtas_call(rtas_token("ibm,get-system-parameter"), 3, 1,
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NULL, CEDE_LATENCY_TOKEN, __pa(&xcede_latency_parameter),
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sizeof(xcede_latency_parameter));
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if (ret) {
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pr_err("xcede: Error parsing CEDE_LATENCY_TOKEN\n");
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return ret;
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}
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payload_size = be16_to_cpu(xcede_latency_parameter.payload_size);
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payload = &xcede_latency_parameter.payload;
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xcede_record_size = payload->record_size + 1;
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if (xcede_record_size != sizeof(struct xcede_latency_record)) {
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pr_err("xcede: Expected record-size %lu. Observed size %u.\n",
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sizeof(struct xcede_latency_record), xcede_record_size);
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return -EINVAL;
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}
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pr_info("xcede: xcede_record_size = %d\n", xcede_record_size);
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/*
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* Since the payload_size includes the last NULL byte and the
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* xcede_record_size, the remaining bytes correspond to array of all
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* cede_latency settings.
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*/
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total_xcede_records_size = payload_size - 2;
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nr_xcede_records = total_xcede_records_size / xcede_record_size;
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for (i = 0; i < nr_xcede_records; i++) {
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struct xcede_latency_record *record = &payload->records[i];
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u64 latency_ticks = be64_to_cpu(record->latency_ticks);
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u8 wake_on_irqs = record->wake_on_irqs;
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u8 hint = record->hint;
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pr_info("xcede: Record %d : hint = %u, latency = 0x%llx tb ticks, Wake-on-irq = %u\n",
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i, hint, latency_ticks, wake_on_irqs);
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}
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return 0;
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}
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#define NR_DEDICATED_STATES 2 /* snooze, CEDE */
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static u8 cede_latency_hint[NR_DEDICATED_STATES];
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static int dedicated_cede_loop(struct cpuidle_device *dev,
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struct cpuidle_driver *drv,
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int index)
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{
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u8 old_latency_hint;
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pseries_idle_prolog();
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get_lppaca()->donate_dedicated_cpu = 1;
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old_latency_hint = get_lppaca()->cede_latency_hint;
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get_lppaca()->cede_latency_hint = cede_latency_hint[index];
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HMT_medium();
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check_and_cede_processor();
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local_irq_disable();
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get_lppaca()->donate_dedicated_cpu = 0;
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get_lppaca()->cede_latency_hint = old_latency_hint;
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pseries_idle_epilog();
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return index;
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}
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static int shared_cede_loop(struct cpuidle_device *dev,
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struct cpuidle_driver *drv,
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int index)
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{
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pseries_idle_prolog();
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/*
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* Yield the processor to the hypervisor. We return if
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* an external interrupt occurs (which are driven prior
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* to returning here) or if a prod occurs from another
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* processor. When returning here, external interrupts
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* are enabled.
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*/
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check_and_cede_processor();
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local_irq_disable();
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pseries_idle_epilog();
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return index;
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}
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/*
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* States for dedicated partition case.
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*/
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static struct cpuidle_state dedicated_states[NR_DEDICATED_STATES] = {
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{ /* Snooze */
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.name = "snooze",
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.desc = "snooze",
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.exit_latency = 0,
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.target_residency = 0,
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.enter = &snooze_loop },
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{ /* CEDE */
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.name = "CEDE",
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.desc = "CEDE",
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.exit_latency = 10,
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.target_residency = 100,
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.enter = &dedicated_cede_loop },
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};
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/*
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* States for shared partition case.
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*/
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static struct cpuidle_state shared_states[] = {
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{ /* Snooze */
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.name = "snooze",
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.desc = "snooze",
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.exit_latency = 0,
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.target_residency = 0,
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.enter = &snooze_loop },
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{ /* Shared Cede */
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.name = "Shared Cede",
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.desc = "Shared Cede",
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.exit_latency = 10,
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.target_residency = 100,
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.enter = &shared_cede_loop },
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};
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static int pseries_cpuidle_cpu_online(unsigned int cpu)
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{
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struct cpuidle_device *dev = per_cpu(cpuidle_devices, cpu);
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if (dev && cpuidle_get_driver()) {
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cpuidle_pause_and_lock();
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cpuidle_enable_device(dev);
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cpuidle_resume_and_unlock();
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}
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return 0;
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}
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static int pseries_cpuidle_cpu_dead(unsigned int cpu)
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{
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struct cpuidle_device *dev = per_cpu(cpuidle_devices, cpu);
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if (dev && cpuidle_get_driver()) {
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cpuidle_pause_and_lock();
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cpuidle_disable_device(dev);
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cpuidle_resume_and_unlock();
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}
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return 0;
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}
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/*
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* pseries_cpuidle_driver_init()
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*/
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static int pseries_cpuidle_driver_init(void)
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{
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int idle_state;
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struct cpuidle_driver *drv = &pseries_idle_driver;
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drv->state_count = 0;
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for (idle_state = 0; idle_state < max_idle_state; ++idle_state) {
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/* Is the state not enabled? */
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if (cpuidle_state_table[idle_state].enter == NULL)
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continue;
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drv->states[drv->state_count] = /* structure copy */
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cpuidle_state_table[idle_state];
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drv->state_count += 1;
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}
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return 0;
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}
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static void __init fixup_cede0_latency(void)
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{
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struct xcede_latency_payload *payload;
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u64 min_latency_us;
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int i;
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min_latency_us = dedicated_states[1].exit_latency; // CEDE latency
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if (parse_cede_parameters())
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return;
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pr_info("cpuidle: Skipping the %d Extended CEDE idle states\n",
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nr_xcede_records);
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payload = &xcede_latency_parameter.payload;
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for (i = 0; i < nr_xcede_records; i++) {
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struct xcede_latency_record *record = &payload->records[i];
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u64 latency_tb = be64_to_cpu(record->latency_ticks);
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u64 latency_us = tb_to_ns(latency_tb) / NSEC_PER_USEC;
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if (latency_us < min_latency_us)
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min_latency_us = latency_us;
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}
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/*
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* By default, we assume that CEDE(0) has exit latency 10us,
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* since there is no way for us to query from the platform.
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*
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* However, if the wakeup latency of an Extended CEDE state is
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* smaller than 10us, then we can be sure that CEDE(0)
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* requires no more than that.
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*
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* Perform the fix-up.
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*/
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if (min_latency_us < dedicated_states[1].exit_latency) {
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u64 cede0_latency = min_latency_us - 1;
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if (cede0_latency <= 0)
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cede0_latency = min_latency_us;
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dedicated_states[1].exit_latency = cede0_latency;
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dedicated_states[1].target_residency = 10 * (cede0_latency);
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pr_info("cpuidle: Fixed up CEDE exit latency to %llu us\n",
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cede0_latency);
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}
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}
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/*
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* pseries_idle_probe()
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* Choose state table for shared versus dedicated partition
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*/
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static int pseries_idle_probe(void)
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{
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if (cpuidle_disable != IDLE_NO_OVERRIDE)
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return -ENODEV;
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if (firmware_has_feature(FW_FEATURE_SPLPAR)) {
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/*
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* Use local_paca instead of get_lppaca() since
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* preemption is not disabled, and it is not required in
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* fact, since lppaca_ptr does not need to be the value
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* associated to the current CPU, it can be from any CPU.
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*/
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if (lppaca_shared_proc(local_paca->lppaca_ptr)) {
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cpuidle_state_table = shared_states;
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max_idle_state = ARRAY_SIZE(shared_states);
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} else {
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fixup_cede0_latency();
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cpuidle_state_table = dedicated_states;
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max_idle_state = NR_DEDICATED_STATES;
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}
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} else
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return -ENODEV;
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if (max_idle_state > 1) {
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snooze_timeout_en = true;
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snooze_timeout = cpuidle_state_table[1].target_residency *
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tb_ticks_per_usec;
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}
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return 0;
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}
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static int __init pseries_processor_idle_init(void)
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{
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int retval;
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retval = pseries_idle_probe();
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if (retval)
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return retval;
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pseries_cpuidle_driver_init();
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retval = cpuidle_register(&pseries_idle_driver, NULL);
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if (retval) {
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printk(KERN_DEBUG "Registration of pseries driver failed.\n");
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return retval;
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}
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retval = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
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"cpuidle/pseries:online",
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pseries_cpuidle_cpu_online, NULL);
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WARN_ON(retval < 0);
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retval = cpuhp_setup_state_nocalls(CPUHP_CPUIDLE_DEAD,
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"cpuidle/pseries:DEAD", NULL,
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pseries_cpuidle_cpu_dead);
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WARN_ON(retval < 0);
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printk(KERN_DEBUG "pseries_idle_driver registered\n");
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return 0;
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}
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device_initcall(pseries_processor_idle_init);
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