Messages in this thread | | | From | Linus Torvalds <> | Date | Sat, 30 Jul 2011 08:32:10 -1000 | Subject | Re: [GIT PULL] Lockless SLUB slowpaths for v3.1-rc1 |
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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:
- *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
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