From: "Paul E. McKenney" <paulmck@kernel.org>
To: Matthew Wilcox <willy@infradead.org>
Cc: Andi Kleen <ak@linux.intel.com>, Feng Tang <feng.tang@intel.com>,
kernel test robot <oliver.sang@intel.com>,
John Stultz <john.stultz@linaro.org>,
Thomas Gleixner <tglx@linutronix.de>,
Stephen Boyd <sboyd@kernel.org>, Jonathan Corbet <corbet@lwn.net>,
Mark Rutland <Mark.Rutland@arm.com>,
Marc Zyngier <maz@kernel.org>,
Xing Zhengjun <zhengjun.xing@linux.intel.com>,
Chris Mason <clm@fb.com>, LKML <linux-kernel@vger.kernel.org>,
Linux Memory Management List <linux-mm@kvack.org>,
lkp@lists.01.org, lkp@intel.com, ying.huang@intel.com,
zhengjun.xing@intel.com
Subject: Re: [clocksource] 8901ecc231: stress-ng.lockbus.ops_per_sec -9.5% regression
Date: Thu, 27 May 2021 14:05:24 -0700 [thread overview]
Message-ID: <20210527210524.GE4397@paulmck-ThinkPad-P17-Gen-1> (raw)
In-Reply-To: <YK/zHMPSZSKrmXC6@casper.infradead.org>
On Thu, May 27, 2021 at 08:29:32PM +0100, Matthew Wilcox wrote:
> On Thu, May 27, 2021 at 12:19:23PM -0700, Paul E. McKenney wrote:
> > On Thu, May 27, 2021 at 12:01:23PM -0700, Andi Kleen wrote:
> > >
> > > > Nevertheless, it is quite possible that real-world use will result in
> > > > some situation requiring that high-stress workloads run on hardware
> > > > not designed to accommodate them, and also requiring that the kernel
> > > > refrain from marking clocksources unstable.
> > > > Therefore, provide an out-of-tree patch that reacts to this situation
> > >
> > > out-of-tree means it will not be submitted?
> > >
> > > I think it would make sense upstream, but perhaps guarded with some option.
> >
> > The reason I do not intend to immediately upstream this patch is that
> > it increases the probability that a real clocksource read-latency issue
> > will be ignored, for example, during hardware bringup. Furthermore,
> > the only known need from it comes from hardware that is, in the words
> > of the stress-ng man page, "poorly designed". And the timing of this
> > email thread leads me to believe that such hardware is not easy to obtain.
>
> I think you're placing a little too much weight on the documentation
> here. It seems that a continuous stream of locked operations executed
> in userspace on a single CPU can cause this problem to occur. If that's
> true all the way out to one guest in a hypervisor can cause problems
> for the hypervisor itself, I think cloud providers everywhere are
> going to want this patch?
Only those cloud provides making heavy use of the aforementioned "poorly
designed" hardware, correct?
Thanx, Paul
> > My thought is therefore to keep this patch out of tree for now.
> > If it becomes clear that long-latency clocksource reads really are
> > a significant issue in their own right (as opposed to merely being a
> > symptom of a hardware or firmware bug), then this patch is available to
> > immediately respond to that issue.
> >
> > And there would then be strong evidence in favor of me biting the bullet,
> > adding the complexity and the additional option (with your Suggested-by),
> > and getting that upstream and into -stable.
> >
> > Seem reasonable?
> >
> > Thanx, Paul
> >
next prev parent reply other threads:[~2021-05-27 21:05 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-21 8:33 [clocksource] 8901ecc231: stress-ng.lockbus.ops_per_sec -9.5% regression kernel test robot
2021-05-21 13:56 ` Paul E. McKenney
2021-05-22 16:08 ` Paul E. McKenney
2021-05-26 6:49 ` Feng Tang
2021-05-26 13:49 ` Paul E. McKenney
2021-05-27 18:29 ` Paul E. McKenney
2021-05-27 19:01 ` Andi Kleen
2021-05-27 19:19 ` Paul E. McKenney
2021-05-27 19:29 ` Matthew Wilcox
2021-05-27 21:05 ` Paul E. McKenney [this message]
2021-05-28 0:58 ` Andi Kleen
2021-06-01 17:10 ` Paul E. McKenney
2021-08-02 6:20 ` Chao Gao
2021-08-02 17:02 ` Paul E. McKenney
2021-08-03 8:58 ` Chao Gao
2021-08-03 13:48 ` Paul E. McKenney
2021-08-05 2:16 ` Chao Gao
2021-08-05 4:03 ` Paul E. McKenney
2021-08-05 4:34 ` Andi Kleen
2021-08-05 15:33 ` Paul E. McKenney
2021-08-05 5:39 ` Chao Gao
2021-08-05 15:37 ` Paul E. McKenney
2021-08-06 2:10 ` Chao Gao
2021-08-06 4:15 ` Paul E. McKenney
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