Messages in this thread | | | Date | Sun, 16 Dec 2007 10:36:21 +0800 | From | Herbert Xu <> | Subject | Re: [PATCH 3/3] [UDP6]: Counter increment on BH mode |
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On Sat, Dec 15, 2007 at 07:43:28PM +0100, Ingo Molnar wrote: > > we could perhaps introduce stat_smp_processor_id(), which signals that > the CPU id is used for statistical purposes and does not have to be > exact? In any case, your patch looks good too.
Unfortunately that doesn't work because we can then have two CPUs trying to update the same counter which may corrupt it.
However, an optimisation is indeed possible with some work. If we can get the address of the per-cpu counter against some sort of a per-cpu base pointer, e.g., %gs on x86, then we can do
incq %gs:(%rax)
where %rax would be the offset with %gs as the base. This would obviate the need for the CPU ID and therefore avoid disabling preemption.
Hmm, wasn't Christoph working on something like that?
Cheers, -- Visit Openswan at http://www.openswan.org/ Email: Herbert Xu ~{PmV>HI~} <herbert@gondor.apana.org.au> Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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