On Wed, Aug 21, 2013 at 02:33:11PM +0200, Peter Zijlstra wrote: > On Wed, Aug 21, 2013 at 01:35:51PM +0200, Oleg Nesterov wrote: > > On 08/21, Peter Zijlstra wrote: > > > > Yes its the right rq, but the wrong time. > > > > Hmm. Just in case, it is not that I think this patch really makes sense, > > but I'd like to understand why do you think it is wrong. > > > But it is not "after it switches out", it is after it switched back. > > D'uh I was being particularly dense it seems :/ > > Yes I think it is correct. You're now trading two atomic ops on a > different cacheline than rq->lock for one atomic op on the rq->lock. > > Might be a win, esp. since hopefully there's a fair chance its the same > runqueue.
The other consideration is that this adds two branches to the normal schedule path. I really don't know what the regular ratio between schedule() and io_schedule() is -- and I suspect it can very much depend on workload -- but it might be a net loss due to that, even if it makes io_schedule() 'lots' cheaper. -- 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/
