Messages in this thread | | | Date | Thu, 11 Apr 2013 12:52:03 -0700 | From | Tejun Heo <> | Subject | Re: [PATCH v2] make dm and dm-crypt forward cgroup context (was: dm-crypt parallelization patches) |
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On Thu, Apr 11, 2013 at 03:49:20PM -0400, Mikulas Patocka wrote: > If the bi_css pointer points to a structure that is shared between > processes, using atomic instruction causes cache line boucing - it doesn't > cost a few instructions, it costs 2-3 hundreds cycles. > > I modified the patch to use new flag BIO_DROP_CGROUP_REFCOUNT to note that > the refcount must be decremented - if the flag is set, refcounts must be > decremented when bio is destroyed, if it is not set, references are > borrowed from upper layer bio. > > It is less bug-prone than the previous patch.
If this becomes an actual bottleneck, the right thing to do is making css ref per-cpu. Please stop messing around with refcounting.
NACK.
-- tejun
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