On Tue, 30 Apr 2013 14:18:24 -0500
Clark Williams <williams@xxxxxxxxxx> wrote:
> On Tue, 30 Apr 2013 19:09:48 +0200
> Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> wrote:
>
> > * Clark Williams | 2013-04-29 16:19:25 [-0500]:
> >
> > >On Mon, 29 Apr 2013 22:12:02 +0200
> > >Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> wrote:
> > >> - suspend / resume seems to program program the timer wrong and wait
> > >> ages until it continues.
> > >
> > >It has to be something we're doing when we apply RT to v3.8.x, since
> > >v3.8.x suspends/resumes with no issues and I was able to suspend and
> > >resume fine with the 3.6-rt series.
> >
> > I think I figured out what is going on or atleast I think I did.
> >
> > This log snippet is from the resume path (from suspend to mem):
> >
> > [ 15.052115] Enabling non-boot CPUs ...
> > [ 15.052115] smpboot: Booting Node 0 Processor 1 APIC 0x1
> > [ 14.841378] Initializing CPU#1
> > [ 42.840017] [sched_delayed] sched: RT throttling activated
> > [ 42.842144] CPU1 is up
> > [ 42.842536] smpboot: Booting Node 0 Processor 2 APIC 0x2
> >
> > Two things happen here:
> > - the time goes backwards from 15.X to 14.X. This is okay because the
> > 14.X is the timestamp from the secondary CPU not - yet synchronized
> > with the bootcpu
> > - the printk with "CPU1 is up" is comming from the boot CPU and
> > according to the timestamp about 28secs passed by. But this did not
> > really happen as the whole procedure took less time.
> >
> > The next thing that happens is that RCU assumes nobody is doing any
> > progress (for almost 28secs) and triggers NMIs & printks to get some
> > attention. I have a trace where
> > - CPU0: arch_trigger_all_cpu_backtrace_handler() => printk()
> > has "lock" and is spinning for logbuf_lock
> >
> > - CPU1: print_cpu_stall() => printk() (spinning for the lock) => NMI =>
> > arch_trigger_all_cpu_backtrace_handler()
> > it may have logbuf_lock and is spinning for "lock"
> >
> > I can't tell if CPU1 got the logbuf_lock at this time but it seemed that
> > it made no progress until I ended it.
> > This NMI releated deadlock is a problem which should also trigger
> > mainline, right?
> >
> > Now, the time jump on the other hand is the real issue here and is
> > RT-only. It looks like we get a big number of timer updates via
> > tick_do_update_jiffies64() because according to ktime_get() that much
> > time really passed by.
> >
> > The sollution seems as simple as
> >
> > From c27eb2e0ab0b5acd96a4b62288976f1b72789b3e Mon Sep 17 00:00:00 2001
> > From: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
> > Date: Tue, 30 Apr 2013 18:53:55 +0200
> > Subject: [PATCH] time/timekeeping: shadow tk->cycle_last together with
> > clock->cycle_last
> >
> > Commit ("timekeeping: Store cycle_last value in timekeeper struct as
> > well") introduced a tk-> based cycle_last values which needs to be reset
> > on resume path as well or else ktime_get() will think that time
> > increased a lot.
> >
> > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
> > ---
> > kernel/time/timekeeping.c | 1 +
> > 1 file changed, 1 insertion(+)
> >
> > diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
> > index 99f943b..688817f 100644
> > --- a/kernel/time/timekeeping.c
> > +++ b/kernel/time/timekeeping.c
> > @@ -777,6 +777,7 @@ static void timekeeping_resume(void)
> > }
> > /* re-base the last cycle value */
> > tk->clock->cycle_last = tk->clock->read(tk->clock);
> > + tk->cycle_last = tk->clock->cycle_last;
> > tk->ntp_error = 0;
> > timekeeping_suspended = 0;
> > timekeeping_update(tk, false, true);
> > --
> > 1.7.10.4
> >
> > So Clark, does this patch fix your problem?
> >
>
> It does seem to! I've got both patches applied right now (your patch to
> vprintk_emit() and the above patch) and it fixes the long delay on my
> lab box. When I get done today (or have a break in the action) I'll try
> it on my laptop to verify.
>
> Thanks Sebastian,
> Clark
Tested on my laptop which now resumes.
Many thanks.
Clark
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