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authorJosh Don <joshdon@google.com>2021-08-27 09:54:38 -0700
committerPeter Zijlstra <peterz@infradead.org>2021-10-05 15:51:35 +0200
commita130e8fbc7de796eb6e680724d87f4737a26d0ac (patch)
tree4adeb41642500b6aca5ddd2b1144a9785e2e591e /fs/proc
parentbc9ffef31bf59819c9fc032178534ff9ed7c4981 (diff)
downloadlwn-a130e8fbc7de796eb6e680724d87f4737a26d0ac.tar.gz
lwn-a130e8fbc7de796eb6e680724d87f4737a26d0ac.zip
fs/proc/uptime.c: Fix idle time reporting in /proc/uptime
/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
Diffstat (limited to 'fs/proc')
-rw-r--r--fs/proc/stat.c4
-rw-r--r--fs/proc/uptime.c14
2 files changed, 11 insertions, 7 deletions
diff --git a/fs/proc/stat.c b/fs/proc/stat.c
index 6561a06ef905..4fb8729a68d4 100644
--- a/fs/proc/stat.c
+++ b/fs/proc/stat.c
@@ -24,7 +24,7 @@
#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;
@@ -46,7 +46,7 @@ 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;
diff --git a/fs/proc/uptime.c b/fs/proc/uptime.c
index 5a1b228964fb..deb99bc9b7e6 100644
--- a/fs/proc/uptime.c
+++ b/fs/proc/uptime.c
@@ -12,18 +12,22 @@ static int uptime_proc_show(struct seq_file *m, void *v)
{
struct timespec64 uptime;
struct timespec64 idle;
- u64 nsec;
+ u64 idle_nsec;
u32 rem;
int i;
- nsec = 0;
- for_each_possible_cpu(i)
- nsec += (__force u64) kcpustat_cpu(i).cpustat[CPUTIME_IDLE];
+ idle_nsec = 0;
+ for_each_possible_cpu(i) {
+ struct kernel_cpustat kcs;
+
+ kcpustat_cpu_fetch(&kcs, i);
+ idle_nsec += get_idle_time(&kcs, i);
+ }
ktime_get_boottime_ts64(&uptime);
timens_add_boottime(&uptime);
- idle.tv_sec = div_u64_rem(nsec, NSEC_PER_SEC, &rem);
+ idle.tv_sec = div_u64_rem(idle_nsec, NSEC_PER_SEC, &rem);
idle.tv_nsec = rem;
seq_printf(m, "%lu.%02lu %lu.%02lu\n",
(unsigned long) uptime.tv_sec,