From: Peter Zijlstra <peterz@infradead.org>
To: Alex Kogan <alex.kogan@oracle.com>
Cc: linux-arch@vger.kernel.org, Hanjun Guo <guohanjun@huawei.com>,
Arnd Bergmann <arnd@arndb.de>,
dave.dice@oracle.com, Jan Glauber <jglauber@marvell.com>,
x86@kernel.org, Will Deacon <will.deacon@arm.com>,
linux@armlinux.org.uk, Steven Sistare <steven.sistare@oracle.com>,
linux-kernel@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
Borislav Petkov <bp@alien8.de>,
hpa@zytor.com, Waiman Long <longman@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
Daniel Jordan <daniel.m.jordan@oracle.com>,
linux-arm-kernel <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v8 4/5] locking/qspinlock: Introduce starvation avoidance into CNA
Date: Tue, 4 Feb 2020 18:27:58 +0100 [thread overview]
Message-ID: <20200204172758.GF14879@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <83762715-F68C-42DF-9B41-C4C48DF6762F@oracle.com>
On Tue, Feb 04, 2020 at 11:54:02AM -0500, Alex Kogan wrote:
> > On Feb 3, 2020, at 10:47 AM, Waiman Long <longman@redhat.com> wrote:
> >
> > On 2/3/20 10:28 AM, Peter Zijlstra wrote:
> >> On Mon, Feb 03, 2020 at 09:59:12AM -0500, Waiman Long wrote:
> >>> On 2/3/20 8:45 AM, Peter Zijlstra wrote:
> >>>> Presumably you have a workload where CNA is actually a win? That is,
> >>>> what inspired you to go down this road? Which actual kernel lock is so
> >>>> contended on NUMA machines that we need to do this?
> There are quite a few actually. files_struct.file_lock, file_lock_context.flc_lock
> and lockref.lock are some concrete examples that get very hot in will-it-scale
> benchmarks.
Right, that's all a variant of banging on the same resources across
nodes. I'm not sure there's anything fundamental we can fix there.
> And then there are spinlocks in __futex_data.queues,
> which get hot when applications have contended (pthread) locks —
> LevelDB is an example.
A numa aware rework of futexes has been on the todo list for years :/
> Our initial motivation was based on an observation that kernel qspinlock is not
> NUMA-aware. So what, you may ask. Much like people realized in the past that
> global spinning is bad for performance, and they switched from ticket lock to
> locks with local spinning (e.g., MCS), I think everyone would agree these days that
> bouncing a lock (and cache lines in general) across numa nodes is similarly bad.
> And as CNA demonstrates, we are easily leaving 2-3x speedups on the table by
> doing just that with the current qspinlock.
Actual benchmarks with performance numbers are required. It helps
motivate the patches as well as gives reviewers clues on how to
reproduce / inspect the claims made.
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next prev parent reply other threads:[~2020-02-04 17:28 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-30 19:40 [PATCH v8 0/5] Add NUMA-awareness to qspinlock Alex Kogan
2019-12-30 19:40 ` [PATCH v8 1/5] locking/qspinlock: Rename mcs lock/unlock macros and make them more generic Alex Kogan
2019-12-30 19:40 ` [PATCH v8 2/5] locking/qspinlock: Refactor the qspinlock slow path Alex Kogan
2019-12-30 19:40 ` [PATCH v8 3/5] locking/qspinlock: Introduce CNA into the slow path of qspinlock Alex Kogan
2020-01-03 22:14 ` Waiman Long
2020-01-06 15:02 ` Alex Kogan
2020-01-21 13:48 ` Peter Zijlstra
2020-01-21 14:42 ` Peter Zijlstra
2019-12-30 19:40 ` [PATCH v8 4/5] locking/qspinlock: Introduce starvation avoidance into CNA Alex Kogan
2020-01-06 15:33 ` Waiman Long
2020-01-21 13:29 ` Peter Zijlstra
2020-01-21 13:50 ` Peter Zijlstra
2020-01-21 21:19 ` Daniel Bristot de Oliveira
2020-01-21 15:45 ` Waiman Long
[not found] ` <3862F8A1-FF9B-40AD-A88E-2C0BA7AF6F58@oracle.com>
2020-01-24 7:52 ` Peter Zijlstra
2020-01-24 14:42 ` Waiman Long
2020-01-24 15:13 ` Peter Zijlstra
2020-01-24 15:19 ` Waiman Long
[not found] ` <8D3AFB47-B595-418C-9568-08780DDC58FF@oracle.com>
[not found] ` <714892cd-d96f-4d41-ae8b-d7b7642a6e3c@redhat.com>
2020-01-25 11:16 ` Peter Zijlstra
[not found] ` <1669BFDE-A1A5-4ED8-B586-035460BBF68A@oracle.com>
[not found] ` <45660873-731a-a810-8c57-1a5a19d266b4@redhat.com>
2020-01-24 18:51 ` Waiman Long
2020-01-25 11:20 ` Peter Zijlstra
2020-01-25 19:57 ` Waiman Long
[not found] ` <693E6287-E37C-4C5D-BE33-B3D813BE505D@oracle.com>
2020-01-24 21:12 ` Waiman Long
2020-01-24 21:27 ` Alex Kogan
2020-01-25 0:38 ` Waiman Long
2020-01-25 11:19 ` Peter Zijlstra
2020-01-30 22:05 ` Alex Kogan
2020-02-03 13:45 ` Peter Zijlstra
2020-02-03 14:59 ` Waiman Long
2020-02-03 15:28 ` Peter Zijlstra
2020-02-03 15:47 ` Waiman Long
[not found] ` <83762715-F68C-42DF-9B41-C4C48DF6762F@oracle.com>
2020-02-04 17:27 ` Peter Zijlstra [this message]
2020-02-04 17:39 ` Waiman Long
2020-02-04 17:53 ` Alex Kogan
2019-12-30 19:40 ` [PATCH v8 5/5] locking/qspinlock: Introduce the shuffle reduction optimization " Alex Kogan
2020-01-22 9:56 ` Peter Zijlstra
2020-01-06 15:48 ` [PATCH v8 0/5] Add NUMA-awareness to qspinlock Waiman Long
2020-01-08 5:09 ` Shijith Thotton
2020-01-21 9:21 ` Shijith Thotton
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