From: Peter Zijlstra <peterz@infradead.org>
To: Waiman Long <longman@redhat.com>
Cc: Ingo Molnar <mingo@redhat.com>, Will Deacon <will.deacon@arm.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] locking/qspinlock_stat: Count instances of nested lock slowpaths
Date: Thu, 18 Oct 2018 11:05:45 +0200 [thread overview]
Message-ID: <20181018090545.GV3121@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <b3931b5a-1695-b273-132c-662f1c8c3a14@redhat.com>
On Wed, Oct 17, 2018 at 05:06:46PM -0400, Waiman Long wrote:
> On 10/17/2018 03:38 AM, Peter Zijlstra wrote:
> > On Tue, Oct 16, 2018 at 09:45:06AM -0400, Waiman Long wrote:
> >> Queued spinlock supports up to 4 levels of lock slowpath nesting -
> >> user context, soft IRQ, hard IRQ and NMI. However, we are not sure how
> >> often the nesting happens. So 3 more per-cpu stat counters are added
> >> to track the number of instances where nesting index goes to 1, 2 and
> >> 3 respectively.
> >>
> >> On a dual-socket 64-core 128-thread Zen server, the following were stat
> >> counter values under different circumstances.
> >>
> >> State slowpath index1 index2 index3
> >> ----- -------- ------ ------ -------
> >> After bootup 1,012,150 82 0 0
> >> After parallel build + perf-top 125,195,009 82 0 0
> > Would probably be good to check a network workload.
>
> Do you have any suggestion of what network workload? I usually don't
> test on network related workload.
Some netperf runs? Be sure to ask the network folks for 2 systems with
at least 10GBe or something.
> The only way to have a nesting level of 3 is when there is lock
> contention in user context, soft IRQ and hard IRQ simultaneously which
> is very rare,
network should be able to trigger a lot of softirq and hardirqs, which
is why I wondered if it could hit significant 3 levels.
But yeah, I played around a bit, and couldn't get my index* numbers to
move at all. I suppose we've gotten really good at avoiding lock
contention for all the benchmarks we care about :-)
next prev parent reply other threads:[~2018-10-18 9:05 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-16 13:45 [PATCH 1/2] locking/qspinlock_stat: Count instances of nested lock slowpaths Waiman Long
2018-10-16 13:45 ` [PATCH 2/2] locking/pvqspinlock: Extend node size when pvqspinlock is configured Waiman Long
2018-10-17 9:12 ` [tip:locking/core] " tip-bot for Waiman Long
2018-10-17 7:38 ` [PATCH 1/2] locking/qspinlock_stat: Count instances of nested lock slowpaths Peter Zijlstra
2018-10-17 21:06 ` Waiman Long
2018-10-18 9:05 ` Peter Zijlstra [this message]
2018-10-17 9:11 ` [tip:locking/core] " tip-bot for Waiman Long
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