From: Peter Zijlstra <peterz@infradead.org>
To: Guo Ren <guoren@kernel.org>
Cc: Alex Kogan <alex.kogan@oracle.com>,
linux@armlinux.org.uk, mingo@redhat.com, will.deacon@arm.com,
arnd@arndb.de, longman@redhat.com, linux-arch@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, tglx@linutronix.de, bp@alien8.de,
hpa@zytor.com, x86@kernel.org, guohanjun@huawei.com,
jglauber@marvell.com, steven.sistare@oracle.com,
daniel.m.jordan@oracle.com, dave.dice@oracle.com
Subject: Re: [PATCH v15 3/6] locking/qspinlock: Introduce CNA into the slow path of qspinlock
Date: Fri, 4 Aug 2023 10:25:31 +0200 [thread overview]
Message-ID: <20230804082531.GL212435@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CAJF2gTQkZ_dVgrdyxRjb=HHgMkBxCkJy0cX_C-FF_ZSQ1ODj-g@mail.gmail.com>
On Fri, Aug 04, 2023 at 09:33:48AM +0800, Guo Ren wrote:
> On Thu, Aug 3, 2023 at 7:57 PM Peter Zijlstra <peterz@infradead.org> wrote:
> > CNA should only show a benefit when there is strong inter-node
> > contention, and in that case it is typically best to fix the kernel side
> > locking.
> >
> > Hence the question as to what lock prompted you to look at this.
> I met the long lock queue situation when the hardware gave an overly
> aggressive store queue merge buffer delay mechanism. See:
> https://lore.kernel.org/linux-riscv/20230802164701.192791-8-guoren@kernel.org/
*groan*, so you're using it to work around 'broken' hardware :-(
Wouldn't that hardware have horrifically bad lock throughput anyway?
Everybody would end up waiting on that store buffer delay.
> This also let me consider improving the efficiency of the long lock
> queue release. For example, if the queue is like this:
>
> (Node0 cpu0) -> (Node1 cpu64) -> (Node0 cpu1) -> (Node1 cpu65) ->
> (Node0 cpu2) -> (Node1 cpu66) -> ...
>
> Then every mcs_unlock would cause a cross-NUMA transaction. But if we
> could make the queue like this:
See, this is where the ARM64 WFE would come in handy; I don't suppose
RISC-V has anything like that?
Also, by the time you have 6 waiters, I'd say the lock is terribly
contended and you should look at improving the lockinh scheme.
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next prev parent reply other threads:[~2023-08-04 8:26 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-14 20:07 [PATCH v15 0/6] Add NUMA-awareness to qspinlock Alex Kogan
2021-05-14 20:07 ` [PATCH v15 1/6] locking/qspinlock: Rename mcs lock/unlock macros and make them more generic Alex Kogan
2021-05-14 20:07 ` [PATCH v15 2/6] locking/qspinlock: Refactor the qspinlock slow path Alex Kogan
2021-05-14 20:07 ` [PATCH v15 3/6] locking/qspinlock: Introduce CNA into the slow path of qspinlock Alex Kogan
2021-09-22 19:25 ` Davidlohr Bueso
2021-09-22 19:52 ` Waiman Long
2023-08-04 1:49 ` Guo Ren
2021-09-30 10:05 ` Barry Song
2023-08-02 23:14 ` Guo Ren
2023-08-03 8:50 ` Peter Zijlstra
2023-08-03 10:28 ` Guo Ren
2023-08-03 11:56 ` Peter Zijlstra
2023-08-04 1:33 ` Guo Ren
2023-08-04 1:38 ` Guo Ren
2023-08-04 8:25 ` Peter Zijlstra [this message]
2023-08-04 14:17 ` Guo Ren
2023-08-04 18:23 ` Peter Zijlstra
2023-08-05 0:19 ` Guo Ren
2021-05-14 20:07 ` [PATCH v15 4/6] locking/qspinlock: Introduce starvation avoidance into CNA Alex Kogan
2021-05-14 20:07 ` [PATCH v15 5/6] locking/qspinlock: Avoid moving certain threads between waiting queues in CNA Alex Kogan
2021-05-14 20:07 ` [PATCH v15 6/6] locking/qspinlock: Introduce the shuffle reduction optimization into CNA Alex Kogan
2021-09-30 9:44 ` [PATCH v15 0/6] Add NUMA-awareness to qspinlock Barry Song
2021-09-30 16:58 ` Waiman Long
2021-09-30 22:57 ` Barry Song
2021-09-30 23:51 ` Alex Kogan
2021-12-13 20:37 ` Alex Kogan
2021-12-15 15:13 ` Alex Kogan
2022-04-11 17:09 ` Alex Kogan
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