Re: [PATCH v3] fsnotify: optimize the case of no parent watcher

From: Jens Axboe <axboe@kernel.dk>
To: Amir Goldstein <amir73il@gmail.com>, Jan Kara <jack@suse.cz>
Cc: Christian Brauner <brauner@kernel.org>, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v3] fsnotify: optimize the case of no parent watcher
Date: Thu, 15 Feb 2024 08:07:32 -0700	[thread overview]
Message-ID: <fcb62332-4e11-4c73-8984-a7f7353fea4e@kernel.dk> (raw)
In-Reply-To: <CAOQ4uxj-waY5KZ20-=F4Gb3F196P-2bc4Q1EDcr_GDraLZHsKQ@mail.gmail.com>

On 2/13/24 12:45 PM, Amir Goldstein wrote:
> Jens,
> 
> If you feel like it, you can see if this branch further improves your
> workloads:
> 
> https://github.com/amir73il/linux/commits/fsnotify-perf/

Baseline is current -git with changes I have for 6.9, so not with the
previous patch. 4 optanes, usually random reads, and being run on a dual
socket Intel(R) Xeon(R) Platinum 8458P  CPU @ 2.7GHz.

IOPS=16.20M, BW=7.91GiB/s, IOS/call=32/31
IOPS=16.20M, BW=7.91GiB/s, IOS/call=32/32
IOPS=16.20M, BW=7.91GiB/s, IOS/call=32/31

and in perf profile, we see:

+    3.16%  io_uring  [kernel.kallsyms]  [k] fsnotify
+    2.04%  io_uring  [kernel.kallsyms]  [k] __fsnotify_parent

with this branch pulled in:

IOPS=17.44M, BW=8.52GiB/s, IOS/call=32/31
IOPS=17.45M, BW=8.52GiB/s, IOS/call=32/31
IOPS=17.45M, BW=8.52GiB/s, IOS/call=32/31

and perf diff shows:

     2.04%     -1.15%  [kernel.kallsyms]  [k] __fsnotify_parent
     3.16%             [kernel.kallsyms]  [k] fsnotify

with a big reduction for __fsnotify_parent() and fsnotify() being
totally gone. In absolute terms, this is all we see in perf profile with
the patch:

+    0.89%  io_uring  [kernel.kallsyms]  [k] __fsnotify_parent

iow, we went from over 5% of added overhead to less than 1%.

-- 
Jens Axboe