Re: Suspend resume problem (WAS Re: [ANNOUNCE] 3.8.10-rt6)

[Clark Williams]

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

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