From: Don Zickus <dzickus@redhat.com>
To: Andi Kleen <ak@linux.intel.com>
Cc: "Liang, Kan" <kan.liang@intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"mingo@kernel.org" <mingo@kernel.org>,
"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
"babu.moger@oracle.com" <babu.moger@oracle.com>,
"atomlin@redhat.com" <atomlin@redhat.com>,
"prarit@redhat.com" <prarit@redhat.com>,
"torvalds@linux-foundation.org" <torvalds@linux-foundation.org>,
"peterz@infradead.org" <peterz@infradead.org>,
"eranian@google.com" <eranian@google.com>,
"acme@redhat.com" <acme@redhat.com>,
"stable@vger.kernel.org" <stable@vger.kernel.org>
Subject: Re: [PATCH V2] kernel/watchdog: fix spurious hard lockups
Date: Thu, 29 Jun 2017 11:44:06 -0400 [thread overview]
Message-ID: <20170629154406.44xo7dnw7btn4gpx@redhat.com> (raw)
In-Reply-To: <20170628201404.GM23705@tassilo.jf.intel.com>
On Wed, Jun 28, 2017 at 01:14:04PM -0700, Andi Kleen wrote:
> It can be a useful debugging tool for a specific class of bugs:
> when kernel software is looping forever.
>
> But if that happens does it really matter how many iterations the
> loop does before it is stopped?
>
> Even the current timeout is essentially eternity in CPU time, and 3x
> eternity is still eternity.
That isn't true. We have customers that test the accuracy and file bugs. I
had to write a RHEL whitepaper a number of years ago explaining why the
softlockup took 62 seconds to fire instead of 60.
Customers were changing the watchdog_thresh when the system slowed down to
purposely trigger a panic (which exposed race conditions leading Uli to
redesign the sysctl interface).
I don't feel like explaining to our customers how we regressed on our
watchdog accuracy. It is exhausting, especially if it is a debug feature.
>
> > The hrtimer increase maintains that and just adds a few more
> > interrupts/second.
>
> Interruptions are a big deal for many people.
Yes, and we probably have customers that will complain on that too.
Either solution is a lose/lose. And yes, we will probably get bit by the
false NMI problems on those Intel boxes. This is why I was preferring a
real solution.
The question is, if the real solution is going to take a while, what is the
least sucky solution for now? Or how do we minimize it to a specific class
of Intel boxes.
Cheers,
Don
next prev parent reply other threads:[~2017-06-29 15:44 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-06-21 14:41 [PATCH V2] kernel/watchdog: fix spurious hard lockups kan.liang
2017-06-21 15:12 ` Thomas Gleixner
2017-06-21 15:47 ` Liang, Kan
2017-06-21 17:40 ` Prarit Bhargava
2017-06-21 17:07 ` Andi Kleen
2017-06-21 19:59 ` Thomas Gleixner
2017-06-21 21:53 ` Thomas Gleixner
2017-06-22 15:33 ` Thomas Gleixner
2017-06-22 15:44 ` Don Zickus
2017-06-22 15:48 ` Liang, Kan
2017-06-23 8:01 ` Thomas Gleixner
2017-06-23 16:29 ` Don Zickus
2017-06-23 21:50 ` Thomas Gleixner
2017-06-26 20:19 ` Don Zickus
2017-06-26 20:30 ` Thomas Gleixner
2017-06-27 20:12 ` Don Zickus
2017-06-27 20:49 ` Liang, Kan
2017-06-27 21:09 ` Don Zickus
2017-06-27 23:48 ` Andi Kleen
2017-06-28 19:00 ` Don Zickus
2017-06-28 20:14 ` Andi Kleen
2017-06-29 15:44 ` Don Zickus [this message]
2017-06-29 16:12 ` Andi Kleen
2017-06-29 16:26 ` Don Zickus
2017-06-29 16:36 ` Andi Kleen
2017-07-17 1:24 ` Liang, Kan
2017-07-17 7:14 ` Thomas Gleixner
2017-07-17 12:18 ` Liang, Kan
2017-07-17 13:13 ` Thomas Gleixner
2017-07-17 14:46 ` Liang, Kan
2017-07-17 15:00 ` Thomas Gleixner
2017-07-17 14:46 ` Don Zickus
2017-08-15 1:16 ` Liang, Kan
2017-08-15 1:28 ` Linus Torvalds
2017-08-15 7:50 ` Thomas Gleixner
2017-08-17 15:45 ` Liang, Kan
2017-08-18 10:39 ` [tip:core/urgent] kernel/watchdog: Prevent false positives with turbo modes tip-bot for Thomas Gleixner
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