On Thu, Jul 26, 2018 at 5:56 PM, Eduardo Valentin <[email protected]> wrote: > System instability are seen during resume from hibernation when system > is under heavy CPU load. This is due to the lack of update of sched > clock data,
Isn't that the actual bug? > and the scheduler would then think that heavy CPU hog > tasks need more time in CPU, causing the system to freeze > during the unfreezing of tasks. For example, threaded irqs, > and kernel processes servicing network interface may be delayed > for several tens of seconds, causing the system to be unreachable. > > Situation like this can be reported by using lockup detectors > such as workqueue lockup detectors: > > [root@ip-172-31-67-114 ec2-user]# echo disk > /sys/power/state > > Message from syslogd@ip-172-31-67-114 at May 7 18:23:21 ... > kernel:BUG: workqueue lockup - pool cpus=0 node=0 flags=0x0 nice=0 stuck for > 57s! > > Message from syslogd@ip-172-31-67-114 at May 7 18:23:21 ... > kernel:BUG: workqueue lockup - pool cpus=1 node=0 flags=0x0 nice=0 stuck for > 57s! > > Message from syslogd@ip-172-31-67-114 at May 7 18:23:21 ... > kernel:BUG: workqueue lockup - pool cpus=3 node=0 flags=0x1 nice=0 stuck for > 57s! > > Message from syslogd@ip-172-31-67-114 at May 7 18:29:06 ... > kernel:BUG: workqueue lockup - pool cpus=3 node=0 flags=0x1 nice=0 stuck for > 403s! > > The fix for this situation is to mark the sched clock as unstable > as early as possible in the resume path, leaving it unstable > for the duration of the resume process. I would rather call it a workaround. > This will force the > scheduler to attempt to align the sched clock across CPUs using > the delta with time of day, updating sched clock data. In a post > hibernation event, we can then mark the sched clock as stable > again, avoiding unnecessary syncs with time of day on systems > in which TSC is reliable. > > Cc: Thomas Gleixner <[email protected]> > Cc: Ingo Molnar <[email protected]> > Cc: "H. Peter Anvin" <[email protected]> > Cc: Peter Zijlstra <[email protected]> > Cc: Dou Liyang <[email protected]> > Cc: Len Brown <[email protected]> > Cc: "Rafael J. Wysocki" <[email protected]> > Cc: Eduardo Valentin <[email protected]> > Cc: "[email protected]" <[email protected]> > Cc: Rajvi Jingar <[email protected]> > Cc: Pavel Tatashin <[email protected]> > Cc: Philippe Ombredanne <[email protected]> > Cc: Kate Stewart <[email protected]> > Cc: Greg Kroah-Hartman <[email protected]> > Cc: [email protected] > Cc: [email protected] > Cc: [email protected] > Signed-off-by: Eduardo Valentin <[email protected]> > --- > > Hey, > > No changes from first attempt, no pressure on resending. The RESEND > tag is just because I missed linux-pm in the first attempt. > > BR, > > arch/x86/kernel/tsc.c | 29 +++++++++++++++++++++++++++++ > include/linux/sched/clock.h | 5 +++++ > kernel/sched/clock.c | 4 ++-- > 3 files changed, 36 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c > index 8ea117f8142e..f197c9742fef 100644 > --- a/arch/x86/kernel/tsc.c > +++ b/arch/x86/kernel/tsc.c > @@ -13,6 +13,7 @@ > #include <linux/percpu.h> > #include <linux/timex.h> > #include <linux/static_key.h> > +#include <linux/suspend.h> > > #include <asm/hpet.h> > #include <asm/timer.h> > @@ -1377,3 +1378,31 @@ unsigned long calibrate_delay_is_known(void) > return 0; > } > #endif > + > +static int tsc_pm_notifier(struct notifier_block *notifier, > + unsigned long pm_event, void *unused) > +{ > + switch (pm_event) { > + case PM_HIBERNATION_PREPARE: > + clear_sched_clock_stable(); > + break; This is too early IMO. This happens before hibernation starts, even before the image is created. > + case PM_POST_HIBERNATION: > + /* Set back to the default */ > + if (!check_tsc_unstable()) > + set_sched_clock_stable(); > + break; > + } > + > + return 0; > +}; If anything like this is the way to go, which honestly I doubt, I would prefer it to be done in hibernate() in the !in_suspend case. But why does it only affect hibernation? Do we do something extra for system-wide suspend/resume that is not done for hibernation?
