On Tue, 2014-09-16 at 16:08 -0400, Peter Hurley wrote: > Hi Jason, > > On 09/16/2014 03:01 PM, Jason Low wrote: > > Commit 9b0fc9c09f1b checks for if there are known active lockers in > > order to avoid write trylocking using expensive cmpxchg() when it > > likely wouldn't get the lock. > > > > However, a subsequent patch was added such that we directly check for > > sem->count == RWSEM_WAITING_BIAS right before trying that cmpxchg(). > > Thus, commit 9b0fc9c09f1b now just adds extra overhead. This patch > > deletes it. > > It would be better to just not reload sem->count, and check the parameter > count == RWSEM_WAITING_BIAS instead. The count parameter is a very recent > load of sem->count (one of which is the latest exclusive read from an > atomic operation), so likely to be just as accurate as a reload of > sem->count without causing more cache line contention.
Hi Peter and Tim, Yes, I also agree. I will send out a new patch with this update. Thanks, Jason -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
