linux-kernel - Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups

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Message-ID: <20170628190008.3ftqq75evhn2hozp@redhat.com>
Date:   Wed, 28 Jun 2017 15:00:08 -0400
From:   Don Zickus <dzickus@...hat.com>
To:     Andi Kleen <ak@...ux.intel.com>
Cc:     "Liang, Kan" <kan.liang@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "mingo@...nel.org" <mingo@...nel.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "babu.moger@...cle.com" <babu.moger@...cle.com>,
        "atomlin@...hat.com" <atomlin@...hat.com>,
        "prarit@...hat.com" <prarit@...hat.com>,
        "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "eranian@...gle.com" <eranian@...gle.com>,
        "acme@...hat.com" <acme@...hat.com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups

On Tue, Jun 27, 2017 at 04:48:22PM -0700, Andi Kleen wrote:
> > I haven't heard back any test result yet.
> > 
> > The above patch looks good to me.
> 
> This needs performance testing.  It may slow down performance or latency sensitive workloads.

More motivation to work through the issues with the proposed real fix? :-)

> 
> > Which workaround do you prefer, the above one or the one checking timestamp?
> 
> I prefer the earlier patch, it has far less risk of performance issues.

But now you are slowing down the nmi_watchdog so much that the
watchdog_thresh hold becomes meaningless, no? (granted the turbo-mode blows
it out of the water too)  So now folks who depend on the 10/5/1/whatever second
reliability lose that.  I think that might be unfair too.

The hrtimer increase maintains that and just adds a few more
interrupts/second.

Cheers,
Don