linux-kernel - Re: [GIT PULL] Lockless SLUB slowpaths for v3.1-rc1

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Sat, 30 Jul 2011 08:32:10 -1000
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Pekka Enberg <penberg@...nel.org>
Cc:	cl@...ux-foundation.org, akpm@...ux-foundation.org,
	rientjes@...gle.com, hughd@...gle.com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [GIT PULL] Lockless SLUB slowpaths for v3.1-rc1

On Sat, Jul 30, 2011 at 8:27 AM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> Do we allocate the page map array sufficiently aligned that we
> actually don't ever have the case of straddling a cacheline? I didn't
> check.

Oh, and another thing worth checking: did somebody actually check the
timings for:

 - *just* the alignment change?

   IOW, maybe some of the netperf improvement isn't from the lockless
path, but exactly from 'struct page' always being in a single
cacheline?

 - check performance with cmpxchg16b *without* the alignment.

   Sometimes especially intel is so good at unaligned accesses that
you wouldn't see an issue. Now, locked ops are usually special (and
crossing cachelines with a locked op is dubious at best), so there may
actually be correctness issues involved too, but it would be
interesting to hear if anybody actually just tried it.

Hmm?

            Linus
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/