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x86, tsc: Remove CPU frequency calibration on AMD 

6b37f5a20c introduced the CPU frequency
calibration code for AMD CPUs whose TSCs didn't increment with the
core's P0 frequency. From F10h, revB onward, however, the TSC increment
rate is denoted by MSRC001_0015[24] and when this bit is set (which
should be done by the BIOS) the TSC increments with the P0 frequency
so the calibration is not needed and booting can be a couple of mcecs
faster on those machines.

Besides, there should be virtually no machines out there which don't
have this bit set, therefore this calibration can be safely removed. It
is a shaky hack anyway since it assumes implicitly that the core is in
P0 when BIOS hands off to the OS, which might not always be the case.

Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>
LKML-Reference: <20100825162823.GE26438@aftab>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
This commit is contained in:
Borislav Petkov 2010-08-25 18:28:23 +02:00 committed by H. Peter Anvin
parent 76be97c1fc
commit acf01734b1
2 changed files with 17 additions and 58 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

17
arch/x86/kernel/cpu/amd.c
View File

@ -412,6 +412,23 @@ static void __cpuinit early_init_amd(struct cpuinfo_x86 *c)
set_cpu_cap(c, X86_FEATURE_EXTD_APICID);
}
#endif
/* We need to do the following only once */
if (c != &boot_cpu_data)
return;
if (cpu_has(c, X86_FEATURE_CONSTANT_TSC)) {
if (c->x86 > 0x10 ||
(c->x86 == 0x10 && c->x86_model >= 0x2)) {
u64 val;
rdmsrl(MSR_K7_HWCR, val);
if (!(val & BIT(24)))
printk(KERN_WARNING FW_BUG "TSC doesn't count "
"with P0 frequency!\n");
}
}
}
static void __cpuinit init_amd(struct cpuinfo_x86 *c)

58
arch/x86/kernel/tsc.c
View File

@ -854,60 +854,6 @@ static void __init init_tsc_clocksource(void)
clocksource_register_khz(&clocksource_tsc, tsc_khz);
}
#ifdef CONFIG_X86_64
/*
* calibrate_cpu is used on systems with fixed rate TSCs to determine
* processor frequency
*/
#define TICK_COUNT 100000000
static unsigned long __init calibrate_cpu(void)
{
int tsc_start, tsc_now;
int i, no_ctr_free;
unsigned long evntsel3 = 0, pmc3 = 0, pmc_now = 0;
unsigned long flags;
for (i = 0; i < 4; i++)
if (avail_to_resrv_perfctr_nmi_bit(i))
break;
no_ctr_free = (i == 4);
if (no_ctr_free) {
WARN(1, KERN_WARNING "Warning: AMD perfctrs busy ... "
"cpu_khz value may be incorrect.\n");
i = 3;
rdmsrl(MSR_K7_EVNTSEL3, evntsel3);
wrmsrl(MSR_K7_EVNTSEL3, 0);
rdmsrl(MSR_K7_PERFCTR3, pmc3);
} else {
reserve_perfctr_nmi(MSR_K7_PERFCTR0 + i);
reserve_evntsel_nmi(MSR_K7_EVNTSEL0 + i);
}
local_irq_save(flags);
/* start measuring cycles, incrementing from 0 */
wrmsrl(MSR_K7_PERFCTR0 + i, 0);
wrmsrl(MSR_K7_EVNTSEL0 + i, 1 << 22 | 3 << 16 | 0x76);
rdtscl(tsc_start);
do {
rdmsrl(MSR_K7_PERFCTR0 + i, pmc_now);
tsc_now = get_cycles();
} while ((tsc_now - tsc_start) < TICK_COUNT);
local_irq_restore(flags);
if (no_ctr_free) {
wrmsrl(MSR_K7_EVNTSEL3, 0);
wrmsrl(MSR_K7_PERFCTR3, pmc3);
wrmsrl(MSR_K7_EVNTSEL3, evntsel3);
} else {
release_perfctr_nmi(MSR_K7_PERFCTR0 + i);
release_evntsel_nmi(MSR_K7_EVNTSEL0 + i);
}
return pmc_now * tsc_khz / (tsc_now - tsc_start);
}
#else
static inline unsigned long calibrate_cpu(void) { return cpu_khz; }
#endif
void __init tsc_init(void)
{
u64 lpj;
@ -926,10 +872,6 @@ void __init tsc_init(void)
return;
}
if (cpu_has(&boot_cpu_data, X86_FEATURE_CONSTANT_TSC) &&
(boot_cpu_data.x86_vendor == X86_VENDOR_AMD))
cpu_khz = calibrate_cpu();
printk("Detected %lu.%03lu MHz processor.\n",
(unsigned long)cpu_khz / 1000,
(unsigned long)cpu_khz % 1000);