On Fri, May 09, 2014 at 10:41:27AM -0600, Jens Axboe wrote: > On 05/09/2014 08:12 AM, Jens Axboe wrote: > > On 05/09/2014 03:17 AM, Matias Bjørling wrote: > >> With multi-million IOPS and multi-node workloads, the atomic_t in_flight > >> tracking becomes a bottleneck. Change the in-flight accounting to per-cpu > >> counters to elevate. > > > > The part stats are a pain in the butt, I've tried to come up with a > > great fix for them too. But I don't think the percpu conversion is > > necessarily the right one. The summing is part of the hotpath, so percpu > > counters aren't necessarily the right way to go. I don't have a better > > answer right now, otherwise it would have been fixed :-) > > Actual data point - this slows my test down ~14% compared to the stock > kernel. Also, if you experiment with this, you need to watch for the > out-of-core users of the part stats (like DM).
I had a try with Matias's patch. Performance actually boost significantly. (there are other cache line issue though, eg, hd_struct_get). Jens, what did you run? part_in_flight() has 3 usages. 2 are for status output, which are cold path. part_round_stats_single() uses it too, but it's a cold path too as we simple data every jiffy. Are you using HZ=1000? maybe we should simple the data every 10ms instead of every jiffy? Thanks, Shaohua -- 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/
