linux-kernel - Re: [PATCH v2] fs: try an opportunistic lookup for O

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Message-ID: <87ikwdtqiy.fsf@linux.intel.com>
Date: Tue, 06 Aug 2024 12:11:49 -0700
From: Andi Kleen <ak@...ux.intel.com>
To: Mateusz Guzik <mjguzik@...il.com>
Cc: Jeff Layton <jlayton@...nel.org>,  Alexander Viro
 <viro@...iv.linux.org.uk>,  Christian Brauner <brauner@...nel.org>,  Jan
 Kara <jack@...e.cz>,  Andrew Morton <akpm@...ux-foundation.org>,  Josef
 Bacik <josef@...icpanda.com>,  linux-fsdevel@...r.kernel.org,
  linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] fs: try an opportunistic lookup for O_CREAT opens too

Mateusz Guzik <mjguzik@...il.com> writes:
>
> I would bench with that myself, but I temporarily don't have handy
> access to bigger hw. Even so, the below is completely optional and
> perhaps more of a suggestion for the future :)
>
> I hacked up the test case based on tests/open1.c.

Don't you need two test cases? One where the file exists and one
where it doesn't. Because the "doesn't exist" will likely be slower
than before because it will do the lookups twice,
and it will likely even slow single threaded.

I assume the penalty will also depend on the number of entries
in the path.

That all seem to be an important considerations in judging the benefits
of the patch.

-Andi