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

[Andi Kleen <andi@firstfloor.org>]

Linus Torvalds <torvalds@linux-foundation.org> writes:

> On Sat, Jul 30, 2011 at 8:27 AM, Linus Torvalds
> <torvalds@linux-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:

I would like to see a followon patch that moves the mem_cgroup
pointer back into struct page. Copying some mem_cgroup people.

>
>  - *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

As Eric pointed out CMPXCHG16B requires alignment, it #GPs otherwise.

-Andi
-- 
ak@linux.intel.com -- Speaking for myself only

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>