Messages in this thread | | | Date | Mon, 5 Dec 2011 09:56:35 +0100 | From | Michal Hocko <> | Subject | Re: Re: [PATCH] proc: Do not overflow get_{idle,iowait}_time for nohz (was: Re: Re: [REGRESSION] [Linux 3.2] top/htop and all other CPU usage) |
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On Fri 02-12-11 20:12:14, Artem S. Tashkinov wrote: > On Dec 2, 2011, Michal Hocko wrote: > > > And the one with a more cleaned up changelog. No functional changes > > --- > > From 107887016b91de59194a93c751d040b05d5e37fe Mon Sep 17 00:00:00 2001 > > From: Michal Hocko <> > > Date: Fri, 2 Dec 2011 16:17:03 +0100 > > Subject: [PATCH] proc: Do not overflow get_{idle,iowait}_time for nohz > > > > Since a25cac51 [proc: Consider NO_HZ when printing idle and iowait times] > > we are reporting idle/io_wait time also while a CPU is tickless. We rely > > on get_{idle,iowait}_time functions to retrieve proper data. > > > > These functions, however, use usecs_to_cputime to translate micro > > seconds time to cputime64_t. This is just an alias to usecs_to_jiffies > > which reduces the data type from u64 to unsigned int and also checks > > whether the given parameter overflows jiffies_to_usecs(MAX_JIFFY_OFFSET) > > and returns MAX_JIFFY_OFFSET in that case. > > > > When do we overflow depends on CONFIG_HZ but especially for > > CONFIG_HZ_300 it is quite low (1431649781) so we are getting > > MAX_JIFFY_OFFSET for >3000s! until we overflow unsigned int. > > Just for reference CONFIG_100 has an overflow window around 20s, > > CONFIG_250 ~8s and CONFIG_1000 ~2s. > > > > This results in a bug when people saw [h]top going mad reporting 100% > > CPU usage even though there was basically no CPU load. The reason was > > simply that /proc/stat stopped reporting idle/io_wait changes (and > > reported MAX_JIFFY_OFFSET) and so the only change happening was for > > user system time. > > > > Let's use nsecs_to_jiffies64 instead which doesn't reduce the precision > > to 32b type and it is much more appropriate for cumulative time values > > (unlike usecs_to_jiffies which intended for timeout calculations). > > > > Signed-off-by: Michal Hocko <mhocko@suse.cz> > > --- > > fs/proc/stat.c | 4 ++-- > > 1 files changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/fs/proc/stat.c b/fs/proc/stat.c > > index 42b274d..2a30d67 100644 > > --- a/fs/proc/stat.c > > +++ b/fs/proc/stat.c > > @@ -32,7 +32,7 @@ static cputime64_t get_idle_time(int cpu) > > idle = kstat_cpu(cpu).cpustat.idle; > > idle = cputime64_add(idle, arch_idle_time(cpu)); > > } else > > - idle = usecs_to_cputime(idle_time); > > + idle = nsecs_to_jiffies64(1000 * idle_time); > > > > return idle; > > } > > @@ -46,7 +46,7 @@ static cputime64_t get_iowait_time(int cpu) > > /* !NO_HZ so we can rely on cpustat.iowait */ > > iowait = kstat_cpu(cpu).cpustat.iowait; > > else > > - iowait = usecs_to_cputime(iowait_time); > > + iowait = nsecs_to_jiffies64(1000 * iowait_time); > > > > return iowait; > > } > > -- > > 1.7.7.3 > > Thank you, this patch has fixed the issue for me. > > Tested-by: Artem S. Tashkinov <t.artem@mailcity.com>
Thanks for retesting!
-- Michal Hocko SUSE Labs SUSE LINUX s.r.o. Lihovarska 1060/12 190 00 Praha 9 Czech Republic
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