From: Will Deacon <will@kernel.org>
To: Hou Tao <houtao1@huawei.com>
Cc: Ard Biesheuvel <ardb@kernel.org>,
peterz@infradead.org, Oleg Nesterov <oleg@redhat.com>,
Ingo Molnar <mingo@redhat.com>, Dennis Zhou <dennis@kernel.org>,
Tejun Heo <tj@kernel.org>, Christoph Lameter <cl@linux.com>,
linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
Jan Kara <jack@suse.cz>
Subject: Re: [RFC PATCH] locking/percpu-rwsem: use this_cpu_{inc|dec}() for read_count
Date: Tue, 29 Sep 2020 18:49:59 +0100 [thread overview]
Message-ID: <20200929174958.GG14317@willie-the-truck> (raw)
In-Reply-To: <522e22a5-98e8-3a99-8f82-dc3789508638@huawei.com>
On Thu, Sep 24, 2020 at 07:55:19PM +0800, Hou Tao wrote:
> The following is the newest performance data:
>
> aarch64 host (4 sockets, 24 cores per sockets)
>
> * v4.19.111
>
> no writer, reader cn | 24 | 48 | 72 | 96
> rate of percpu_down_read/percpu_up_read per second |
> default: use __this_cpu_inc|dec() | 166129572 | 166064100 | 165963448 | 165203565
> patched: use this_cpu_inc|dec() | 87727515 | 87698669 | 87675397 | 87337435
> modified: local_irq_save + __this_cpu_inc|dec() | 15470357 | 15460642 | 15439423 | 15377199
>
> * v4.19.111+ [1]
>
> modified: use this_cpu_inc|dec() + LSE atomic | 8224023 | 8079416 | 7883046 | 7820350
>
> * 5.9-rc6
>
> no writer, reader cn | 24 | 48 | 72 | 96
> rate of percpu_down_read/percpu_up_read per second |
> reverted: use __this_cpu_inc|dec() + revert 91fc957c| 169664061 | 169481176 | 168493488 | 168844423
> reverted: use __this_cpu_inc|dec() | 78355071 | 78294285 | 78026030 | 77860492
> modified: use this_cpu_inc|dec() + no LSE atomic | 64291101 | 64259867 | 64223206 | 63992316
> default: use this_cpu_inc|dec() + LSE atomic | 16231421 | 16215618 | 16188581 | 15959290
>
> It seems that enabling LSE atomic has a negative impact on performance under this test scenario.
>
> And it is astonished to me that for my test scenario the performance of v5.9-rc6 is just one half of v4.19.
> The bisect finds the culprit is 91fc957c9b1d6 ("arm64/bpf: don't allocate BPF JIT programs in module memory").
> If reverting the patch brute-forcibly under 5.9-rc6 [2], the performance will be the same with
> v4.19.111 (169664061 vs 166129572). I have had the simplified test module [3] and .config attached [4],
> so could you please help to check what the problem is ?
I have no idea how that patch can be responsible for this :/ Have you
confirmed that the bisection is not bogus?
Ard, do you have any ideas?
Will
next prev parent reply other threads:[~2020-09-29 17:50 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-15 14:07 [RFC PATCH] locking/percpu-rwsem: use this_cpu_{inc|dec}() for read_count Hou Tao
2020-09-15 15:06 ` peterz
2020-09-15 15:31 ` Oleg Nesterov
2020-09-15 15:51 ` peterz
2020-09-15 16:03 ` peterz
2020-09-15 16:11 ` Will Deacon
2020-09-15 18:11 ` peterz
2020-09-16 8:20 ` Will Deacon
2020-09-15 16:47 ` Oleg Nesterov
2020-09-16 12:32 ` Hou Tao
2020-09-16 12:51 ` peterz
2020-09-17 8:48 ` Will Deacon
2020-09-24 11:55 ` Hou Tao
2020-09-29 17:49 ` Will Deacon [this message]
2020-09-29 18:07 ` Ard Biesheuvel
2020-09-17 10:51 ` Boaz Harrosh
2020-09-17 12:01 ` Oleg Nesterov
2020-09-17 12:48 ` Matthew Wilcox
2020-09-17 13:22 ` peterz
2020-09-17 13:34 ` Oleg Nesterov
2020-09-17 13:46 ` Boaz Harrosh
2020-09-17 14:46 ` Christoph Hellwig
2020-09-18 9:07 ` Jan Kara
2020-09-18 10:01 ` peterz
2020-09-18 10:04 ` peterz
2020-09-18 10:07 ` peterz
2020-09-18 10:12 ` peterz
2020-09-18 10:48 ` Oleg Nesterov
2020-09-18 11:03 ` peterz
2020-09-18 13:09 ` Oleg Nesterov
2020-09-18 13:26 ` Jan Kara
2020-09-20 23:49 ` Dave Chinner
2020-09-18 8:36 ` [tip: locking/urgent] locking/percpu-rwsem: Use this_cpu_{inc,dec}() " tip-bot2 for Hou Tao
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