From: Peter Zijlstra <peterz@infradead.org>
To: Anchal Agarwal <anchalag@amazon.com>
Cc: tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
hpa@zytor.com, x86@kernel.org, boris.ostrovsky@oracle.com,
jgross@suse.com, linux-pm@vger.kernel.org, linux-mm@kvack.org,
kamatam@amazon.com, sstabellini@kernel.org,
konrad.wilk@oracle.co, roger.pau@citrix.com, axboe@kernel.dk,
davem@davemloft.net, rjw@rjwysocki.net, len.brown@intel.com,
pavel@ucw.cz, eduval@amazon.com, sblbir@amazon.com,
xen-devel@lists.xenproject.org, vkuznets@redhat.com,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
Woodhouse@dev-dsk-anchalag-2a-9c2d1d96.us-west-2.amazon.com,
dwmw@amazon.co.uk, fllinden@amaozn.com
Subject: Re: [RFC PATCH V2 11/11] x86: tsc: avoid system instability in hibernation
Date: Wed, 8 Jan 2020 11:50:11 +0100 [thread overview]
Message-ID: <20200108105011.GY2827@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20200107234526.GA19034@dev-dsk-anchalag-2a-9c2d1d96.us-west-2.amazon.com>
On Tue, Jan 07, 2020 at 11:45:26PM +0000, Anchal Agarwal wrote:
> From: Eduardo Valentin <eduval@amazon.com>
>
> 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, 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.
> 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. 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.
This makes no frigging sense what so bloody ever. If the clock is
stable, we don't care about sched_clock_data. When it is stable you get
a linear function of the TSC without complicated bits on.
When it is unstable, only then do we care about the sched_clock_data.
> Reviewed-by: Erik Quanstrom <quanstro@amazon.com>
> Reviewed-by: Frank van der Linden <fllinden@amazon.com>
> Reviewed-by: Balbir Singh <sblbir@amazon.com>
> Reviewed-by: Munehisa Kamata <kamatam@amazon.com>
> Tested-by: Anchal Agarwal <anchalag@amazon.com>
> Signed-off-by: Eduardo Valentin <eduval@amazon.com>
> ---
NAK, the code very much relies on never getting marked stable again
after it gets set to unstable.
> diff --git a/kernel/sched/clock.c b/kernel/sched/clock.c
> index 1152259a4ca0..374d40e5b1a2 100644
> --- a/kernel/sched/clock.c
> +++ b/kernel/sched/clock.c
> @@ -116,7 +116,7 @@ static void __scd_stamp(struct sched_clock_data *scd)
> scd->tick_raw = sched_clock();
> }
>
> -static void __set_sched_clock_stable(void)
> +void set_sched_clock_stable(void)
> {
> struct sched_clock_data *scd;
>
> @@ -236,7 +236,7 @@ static int __init sched_clock_init_late(void)
> smp_mb(); /* matches {set,clear}_sched_clock_stable() */
>
> if (__sched_clock_stable_early)
> - __set_sched_clock_stable();
> + set_sched_clock_stable();
>
> return 0;
> }
> --
> 2.15.3.AMZN
>
next prev parent reply other threads:[~2020-01-08 10:51 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-07 23:45 [RFC PATCH V2 11/11] x86: tsc: avoid system instability in hibernation Anchal Agarwal
2020-01-08 10:50 ` Peter Zijlstra [this message]
2020-01-10 15:35 ` Eduardo Valentin
2020-01-13 10:16 ` Peter Zijlstra
2020-01-13 11:43 ` Singh, Balbir
2020-01-13 11:48 ` Rafael J. Wysocki
2020-01-13 12:42 ` Peter Zijlstra
2020-01-13 21:50 ` Rafael J. Wysocki
2020-01-13 23:30 ` Rafael J. Wysocki
2020-01-14 19:29 ` Anchal Agarwal
2020-01-22 20:07 ` Anchal Agarwal
2020-01-23 16:27 ` Boris Ostrovsky
2020-01-13 13:01 ` [Xen-devel] " Andrew Cooper
2020-01-13 13:54 ` David Woodhouse
2020-01-13 15:02 ` Singh, Balbir
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