linux-kernel - Re: [BUG, bisect] hrtimer: severe lag after suspend & resume

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Message-ID: <alpine.DEB.2.11.1506041319580.7118@nanos>
Date:	Thu, 4 Jun 2015 13:22:45 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Jeremiah Mahler <jmmahler@...il.com>
cc:	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	John Stultz <john.stultz@...aro.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [BUG, bisect] hrtimer: severe lag after suspend & resume

On Wed, 3 Jun 2015, Jeremiah Mahler wrote:
> After a fresh boot, the Chrome web browser behaves normally.  Pages
> load quickly and scroll fast.  Even image heavy sites such as
> images.google.com work fine.  However, after a suspend and resume
> cycle, Chrome becomes very slow.  Pages take ten seconds or more to
> load.  The scroll bars and buttons are almost completely
> unresponsive.  Interestingly, I can run Firefox on the same sites
> and it has no issue whatsoever.

Weird.
 
> I have bisected the kernel and found that the following commit
> introduced the bug.  It is present in the latest linux-next (20150602).
> 
>   From 868a3e915f7f5eba8f8cb4f7da2276760807c51c Mon Sep 17 00:00:00 2001
>   From: Thomas Gleixner <tglx@...utronix.de>
>   Date: Tue, 14 Apr 2015 21:08:37 +0000
>   Subject: [PATCH] hrtimer: Make offset update smarter
>   
>   On every tick/hrtimer interrupt we update the offset variables of the
>   clock bases. That's silly because these offsets change very seldom.
>   
>   Add a sequence counter to the time keeping code which keeps track of
>   the offset updates (clock_was_set()). Have a sequence cache in the
>   hrtimer cpu bases to evaluate whether the offsets must be updated or
>   not. This allows us later to avoid pointless cacheline pollution.

I had to wrap my head around that for quite a while, but I think I
have decoded the issue. Can you please test the patch below whether it
solves your problem?

Thanks,

	tglx

------------------------>

diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 278d4b36fd94..e9dfcd0b8c41 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -1492,6 +1492,12 @@ static void init_hrtimers_cpu(int cpu)
 
 	cpu_base->cpu = cpu;
 	hrtimer_init_hres(cpu_base);
+	/*
+	 * Force an update by setting the clock was set sequence to an
+	 * odd value.
+	 */
+	cpu_base->clock_was_set_seq = 1;
+	hrtimer_update_base(cpu_base);
 }
 
 #ifdef CONFIG_HOTPLUG_CPU
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 90ed5db67c1d..c97710137a9e 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -593,7 +593,7 @@ static void timekeeping_update(struct timekeeper *tk, unsigned int action)
 	update_fast_timekeeper(&tk->tkr_raw,  &tk_fast_raw);
 
 	if (action & TK_CLOCK_WAS_SET)
-		tk->clock_was_set_seq++;
+		tk->clock_was_set_seq += 2;
 }
 
 /**
--
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