Messages in this thread |  | | Date | Wed, 13 Nov 2013 09:40:48 -0800 | From | John Stultz <> | Subject | Re: performance regressions by "seqcount: Add lockdep functionality to seqcount/seqlock structures" |
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On 11/13/2013 01:14 AM, Yuanhan Liu wrote: > Hi, > > FYI, we found some performance regressions caused by commit 1ca7d67c > ("seqcount: Add lockdep functionality to seqcount/seqlock structures")
So this is expected. seqlock readers are usually very very cheap operations, and we're now doing lockdep tracking on every iteration around the loop. As the lockdep help states:
| If you say Y here, the lock dependency engine will do | | additional runtime checks to debug itself, at the price | | of more runtime overhead.
So now since we're also tracking seqlocks in addition to spinlocks, it creates more overhead.
Disabling CONFIG_LOCKDEP should restore performance.
thanks -john
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