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a130e8fbc7
/proc/uptime reports idle time by reading the CPUTIME_IDLE field from
the per-cpu kcpustats. However, on NO_HZ systems, idle time is not
continually updated on idle cpus, leading this value to appear
incorrectly small.
/proc/stat performs an accounting update when reading idle time; we
can use the same approach for uptime.
With this patch, /proc/stat and /proc/uptime now agree on idle time.
Additionally, the following shows idle time tick up consistently on an
idle machine:
(while true; do cat /proc/uptime; sleep 1; done) | awk '{print $2-prev; prev=$2}'
Reported-by: Luigi Rizzo <lrizzo@google.com>
Signed-off-by: Josh Don <joshdon@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://lkml.kernel.org/r/20210827165438.3280779-1-joshdon@google.com
45 lines
1 KiB
C
45 lines
1 KiB
C
// SPDX-License-Identifier: GPL-2.0
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#include <linux/fs.h>
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#include <linux/init.h>
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#include <linux/proc_fs.h>
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#include <linux/sched.h>
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#include <linux/seq_file.h>
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#include <linux/time.h>
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#include <linux/time_namespace.h>
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#include <linux/kernel_stat.h>
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static int uptime_proc_show(struct seq_file *m, void *v)
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{
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struct timespec64 uptime;
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struct timespec64 idle;
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u64 idle_nsec;
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u32 rem;
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int i;
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idle_nsec = 0;
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for_each_possible_cpu(i) {
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struct kernel_cpustat kcs;
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kcpustat_cpu_fetch(&kcs, i);
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idle_nsec += get_idle_time(&kcs, i);
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}
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ktime_get_boottime_ts64(&uptime);
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timens_add_boottime(&uptime);
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idle.tv_sec = div_u64_rem(idle_nsec, NSEC_PER_SEC, &rem);
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idle.tv_nsec = rem;
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seq_printf(m, "%lu.%02lu %lu.%02lu\n",
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(unsigned long) uptime.tv_sec,
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(uptime.tv_nsec / (NSEC_PER_SEC / 100)),
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(unsigned long) idle.tv_sec,
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(idle.tv_nsec / (NSEC_PER_SEC / 100)));
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return 0;
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}
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static int __init proc_uptime_init(void)
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{
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proc_create_single("uptime", 0, NULL, uptime_proc_show);
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return 0;
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}
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fs_initcall(proc_uptime_init);
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