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fs/proc/uptime.c: Fix idle time reporting in /proc/uptime

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[ Upstream commit a130e8fbc7de796eb6e680724d87f4737a26d0ac ]

/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
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Josh Don
2021-08-27 09:54:38 -07:00
committed by Greg Kroah-Hartman
parent 6e242c557a
commit f09e1a2d2c
3 changed files with 12 additions and 7 deletions
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4
fs/proc/stat.c
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@@ -23,7 +23,7 @@
#ifdef arch_idle_time
static u64 get_idle_time(struct kernel_cpustat *kcs, int cpu)
u64 get_idle_time(struct kernel_cpustat *kcs, int cpu)
{
u64 idle;
@@ -45,7 +45,7 @@ static u64 get_iowait_time(struct kernel_cpustat *kcs, int cpu)
#else
static u64 get_idle_time(struct kernel_cpustat *kcs, int cpu)
u64 get_idle_time(struct kernel_cpustat *kcs, int cpu)
{
u64 idle, idle_usecs = -1ULL;