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: Mon, 3 Feb 2020 14:45:40 +0100 [thread overview]
Message-ID: <20200203134540.GA14879@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <F32558D8-4ACB-483A-AB4C-F565003A02E7@oracle.com>
On Thu, Jan 30, 2020 at 05:05:28PM -0500, Alex Kogan wrote:
>
> > On Jan 25, 2020, at 6:19 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> >
> > On Fri, Jan 24, 2020 at 01:19:05PM -0500, Alex Kogan wrote:
> >
> >> Is there a lightweight way to identify such a “prioritized” thread?
> >
> > No; people might for instance care about tail latencies between their
> > identically spec'ed worker tasks.
>
> I would argue that those users need to tune/reduce the intra-node handoff
> threshold for their needs. Or disable CNA altogether.
I really don't like boot time arguments (or tunables in generic) for a
machine to work as it should.
The default really should 'just work'.
> In general, Peter, seems like you are not on board with the way Longman
> suggested to handle prioritized threads. Am I right?
Right.
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?
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WARNING: multiple messages have this Message-ID (diff)
From: Peter Zijlstra <peterz@infradead.org>
To: Alex Kogan <alex.kogan@oracle.com>
Cc: Waiman Long <longman@redhat.com>,
linux@armlinux.org.uk, Ingo Molnar <mingo@redhat.com>,
Will Deacon <will.deacon@arm.com>, Arnd Bergmann <arnd@arndb.de>,
linux-arch@vger.kernel.org,
linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
linux-kernel@vger.kernel.org,
Thomas Gleixner <tglx@linutronix.de>,
Borislav Petkov <bp@alien8.de>,
hpa@zytor.com, x86@kernel.org, Hanjun Guo <guohanjun@huawei.com>,
Jan Glauber <jglauber@marvell.com>,
Steven Sistare <steven.sistare@oracle.com>,
Daniel Jordan <daniel.m.jordan@oracle.com>,
dave.dice@oracle.com
Subject: Re: [PATCH v8 4/5] locking/qspinlock: Introduce starvation avoidance into CNA
Date: Mon, 3 Feb 2020 14:45:40 +0100 [thread overview]
Message-ID: <20200203134540.GA14879@hirez.programming.kicks-ass.net> (raw)
Message-ID: <20200203134540.fea6t6tRfEqEpVK5lSlgBKGg7Uttek_0TQNdQ00x-lE@z> (raw)
In-Reply-To: <F32558D8-4ACB-483A-AB4C-F565003A02E7@oracle.com>
On Thu, Jan 30, 2020 at 05:05:28PM -0500, Alex Kogan wrote:
>
> > On Jan 25, 2020, at 6:19 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> >
> > On Fri, Jan 24, 2020 at 01:19:05PM -0500, Alex Kogan wrote:
> >
> >> Is there a lightweight way to identify such a “prioritized” thread?
> >
> > No; people might for instance care about tail latencies between their
> > identically spec'ed worker tasks.
>
> I would argue that those users need to tune/reduce the intra-node handoff
> threshold for their needs. Or disable CNA altogether.
I really don't like boot time arguments (or tunables in generic) for a
machine to work as it should.
The default really should 'just work'.
> In general, Peter, seems like you are not on board with the way Longman
> suggested to handle prioritized threads. Am I right?
Right.
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?
next prev parent reply other threads:[~2020-02-03 13:45 UTC|newest]
Thread overview: 72+ 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 ` 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 ` 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 ` Alex Kogan
2019-12-30 19:40 ` [PATCH v8 3/5] locking/qspinlock: Introduce CNA into the slow path of qspinlock Alex Kogan
2019-12-30 19:40 ` Alex Kogan
2020-01-03 22:14 ` Waiman Long
2020-01-03 22:14 ` Waiman Long
2020-01-06 15:02 ` Alex Kogan
2020-01-06 15:02 ` Alex Kogan
2020-01-21 13:48 ` Peter Zijlstra
2020-01-21 13:48 ` Peter Zijlstra
2020-01-21 14:42 ` 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
2019-12-30 19:40 ` Alex Kogan
2020-01-06 15:33 ` Waiman Long
2020-01-06 15:33 ` Waiman Long
2020-01-21 13:29 ` Peter Zijlstra
2020-01-21 13:29 ` Peter Zijlstra
2020-01-21 13:50 ` Peter Zijlstra
2020-01-21 13:50 ` Peter Zijlstra
2020-01-21 21:19 ` Daniel Bristot de Oliveira
2020-01-21 21:19 ` Daniel Bristot de Oliveira
2020-01-21 15:45 ` Waiman Long
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 7:52 ` Peter Zijlstra
2020-01-24 14:42 ` Waiman Long
2020-01-24 15:13 ` Peter Zijlstra
2020-01-24 15:13 ` Peter Zijlstra
2020-01-24 15:19 ` Waiman Long
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
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
2020-01-24 18:51 ` Waiman Long
2020-01-25 11:20 ` Peter Zijlstra
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 21:12 ` Waiman Long
2020-01-24 21:27 ` Alex Kogan
2020-01-25 0:38 ` Waiman Long
2020-01-25 0:38 ` Waiman Long
2020-01-25 11:19 ` Peter Zijlstra
2020-01-25 11:19 ` Peter Zijlstra
2020-01-30 22:05 ` Alex Kogan
2020-02-03 13:45 ` Peter Zijlstra [this message]
2020-02-03 13:45 ` Peter Zijlstra
2020-02-03 14:59 ` Waiman Long
2020-02-03 14:59 ` Waiman Long
2020-02-03 15:28 ` Peter Zijlstra
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
2020-02-04 17:27 ` Peter Zijlstra
2020-02-04 17:39 ` Waiman Long
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
2019-12-30 19:40 ` Alex Kogan
2020-01-22 9:56 ` Peter Zijlstra
2020-01-22 9:56 ` Peter Zijlstra
2020-01-06 15:48 ` [PATCH v8 0/5] Add NUMA-awareness to qspinlock Waiman Long
2020-01-06 15:48 ` Waiman Long
2020-01-08 5:09 ` Shijith Thotton
2020-01-08 5:09 ` Shijith Thotton
2020-01-21 9:21 ` Shijith Thotton
2020-01-21 9:21 ` Shijith Thotton
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