linux-kernel - Re: [rfc][patch 1/3] slub: fix small HWCACHE

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:	Wed, 5 Mar 2008 01:08:20 +0100
From:	Nick Piggin <npiggin@...e.de>
To:	Christoph Lameter <clameter@....com>
Cc:	Pekka Enberg <penberg@...helsinki.fi>, netdev@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	yanmin_zhang@...ux.intel.com, David Miller <davem@...emloft.net>,
	Eric Dumazet <dada1@...mosbay.com>
Subject: Re: [rfc][patch 1/3] slub: fix small HWCACHE_ALIGN alignment

On Mon, Mar 03, 2008 at 01:32:54PM -0800, Christoph Lameter wrote:
> On Mon, 3 Mar 2008, Pekka Enberg wrote:
> 
> > Well, not my definition either but SLAB has guaranteed that for small
> > objects in the past, so I think Nick has a point here. However, with
> > all this back and forth, I've lost track why this matters. I suppose
> > it causes regression on some workload?
> 
> Well the guarantee can only be exploited if you would check the cacheline 
> sizes and the object size from the code that creates the slab cache. 
> Basically you would have to guestimate what the slab allocator is doing.
> 
> So the guarantee is basically meaningless. If the object is larger than a 
> cacheline then this will never work.

Of course it works. It fits the object into the fewest number of cachelines
possible. If you need to be accessing such objects in a random manner, then
for highest performance you want to touch as few cachelines as possible.

--
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/