From: Matthew Wilcox <willy@infradead.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Christian Brauner <brauner@kernel.org>,
Al Viro <viro@zeniv.linux.org.uk>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
the arch/x86 maintainers <x86@kernel.org>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: FYI: path walking optimizations pending for 6.11
Date: Wed, 19 Jun 2024 21:45:33 +0100 [thread overview]
Message-ID: <ZnNDbe8GZJ1gNuzk@casper.infradead.org> (raw)
In-Reply-To: <CAHk-=whHvMbfL2ov1MRbT9QfebO2d6-xXi1ynznCCi-k_m6Q0w@mail.gmail.com>
On Wed, Jun 19, 2024 at 01:25:02PM -0700, Linus Torvalds wrote:
> For example, making d_hash() avoid indirection just means that now
> pretty much _all_ the cost of __d_lookup_rcu() is in the cache misses
> on the hash table itself. Which was always the bulk of it. And on my
> arm64 machine, it turns out that the best optimization for the load I
> tested would be to make that hash table smaller to actually be a bit
> denser in the cache, But that's such a load-dependent optimization
> that I'm not doing this.
>
> Tuning the hash table size or data structure cacheline layouts might
> be worthwhile - and likely a bigger deal - but is _not_ what these
> patches are about.
Funnily, I'm working on rosebush v2 today. It's in no shape to send out
(it's failing ~all of its selftests) but *should* greatly improve the
cache friendliness of the hash table. And it's being written with the
dcache as its first customer.
next prev parent reply other threads:[~2024-06-19 20:45 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-06-19 20:25 FYI: path walking optimizations pending for 6.11 Linus Torvalds
2024-06-19 20:45 ` Matthew Wilcox [this message]
2024-06-19 22:08 ` Linus Torvalds
2024-06-20 18:53 ` Kent Overstreet
2024-06-21 20:04 ` Matthew Wilcox
2024-06-21 20:53 ` Linus Torvalds
2024-06-20 7:53 ` Arnd Bergmann
2024-06-20 17:25 ` Linus Torvalds
2024-07-09 10:04 ` Mark Rutland
2024-07-09 14:28 ` Linus Torvalds
2024-07-09 16:24 ` Linus Torvalds
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