Le Tue, Mar 03, 2026 at 04:47:45PM +0530, Shrikanth Hegde a écrit : > > > On 2/6/26 7:52 PM, Frederic Weisbecker wrote: > > The dyntick-idle steal time is currently accounted when the tick > > restarts but the stolen idle time is not substracted from the idle time > > that was already accounted. This is to avoid observing the idle time > > going backward as the dyntick-idle cputime accessors can't reliably know > > in advance the stolen idle time. > > > > In order to maintain a forward progressing idle cputime while > > substracting idle steal time from it, keep track of the previously > > accounted idle stolen time and substract it from _later_ idle cputime > > accounting. > > > > s/substract/subtract ?
Right. > > > Signed-off-by: Frederic Weisbecker <[email protected]> > > --- > > include/linux/kernel_stat.h | 1 + > > kernel/sched/cputime.c | 21 +++++++++++++++------ > > 2 files changed, 16 insertions(+), 6 deletions(-) > > > > diff --git a/include/linux/kernel_stat.h b/include/linux/kernel_stat.h > > index 512104b0ff49..24a54a6151ba 100644 > > --- a/include/linux/kernel_stat.h > > +++ b/include/linux/kernel_stat.h > > @@ -39,6 +39,7 @@ struct kernel_cpustat { > > bool idle_elapse; > > seqcount_t idle_sleeptime_seq; > > u64 idle_entrytime; > > + u64 idle_stealtime; > > #endif > > u64 cpustat[NR_STATS]; > > }; > > diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c > > index 92fa2f037b6e..7e79288eb327 100644 > > --- a/kernel/sched/cputime.c > > +++ b/kernel/sched/cputime.c > > @@ -424,19 +424,25 @@ static inline void > > irqtime_account_process_tick(struct task_struct *p, int user_ > > static void kcpustat_idle_stop(struct kernel_cpustat *kc, u64 now) > > { > > u64 *cpustat = kc->cpustat; > > - u64 delta; > > + u64 delta, steal, steal_delta; > > if (!kc->idle_elapse) > > return; > > delta = now - kc->idle_entrytime; > > + steal = steal_account_process_time(delta); > > write_seqcount_begin(&kc->idle_sleeptime_seq); > > + steal_delta = min_t(u64, kc->idle_stealtime, delta); > > + delta -= steal_delta; > > I didn;t get this logic. Why do we need idle_stealtime? > > Lets say 10ms was steal time and 50ms was delta. but idle_stealtime is > sum of past accumulated steal time. we only need to subtract steal time there > no? > > Shouldn't this be delta -= steal ? That would be a risk to observe backward idle accounting: Time CPU 0 CPU 1 ---- ----- ----- 0 sec kcpustat_idle_start() <#VMEXIT> ... 1 sec </#VMEXIT> arch_cpu_idle() // returns 2 2 sec kcpustat_idle_stop() kcpustat_field(CPUTIME_IDLE, 0) cpustat[CPUTIME_IDLE] = 2 - 1 // returns 1 kcpustat_field(CPUTIME_IDLE, 0) We could instead read remotely the paravirt clock, but then steal_account_process_time() would need to always hold the ->idle_sleeptime_seq, though it should happen to work without given the ordering. Anyway to avoid any surprise I accumulate the steal time of an idle cycle to be substracted on the next idle cycle. Thanks. -- Frederic Weisbecker SUSE Labs
