On 2011-07-22 07:14, Shaohua Li wrote: > On Fri, 2011-07-22 at 03:32 +0800, Jens Axboe wrote: >> On 2011-07-20 08:49, Shaohua Li wrote: >>> On Wed, 2011-07-20 at 14:30 +0800, Minchan Kim wrote: >>>> On Wed, Jul 20, 2011 at 3:10 PM, Shaohua Li <shaohua.li@xxxxxxxxx> wrote: >>>>> On Wed, 2011-07-20 at 13:53 +0800, Minchan Kim wrote: >>>>>> On Wed, Jul 20, 2011 at 11:53 AM, Shaohua Li <shaohua.li@xxxxxxxxx> wrote: >>>>>>> per-task block plug can reduce block queue lock contention and increase request >>>>>>> merge. Currently page reclaim doesn't support it. I originally thought page >>>>>>> reclaim doesn't need it, because kswapd thread count is limited and file cache >>>>>>> write is done at flusher mostly. >>>>>>> When I test a workload with heavy swap in a 4-node machine, each CPU is doing >>>>>>> direct page reclaim and swap. This causes block queue lock contention. In my >>>>>>> test, without below patch, the CPU utilization is about 2% ~ 7%. With the >>>>>>> patch, the CPU utilization is about 1% ~ 3%. Disk throughput isn't changed. >>>>>> >>>>>> Why doesn't it enhance through? >>>>> throughput? The disk isn't that fast. We already can make it run in full >>>> >>>> Yes. Sorry for the typo. >>>> >>>>> speed, CPU isn't bottleneck here. >>>> >>>> But you try to optimize CPU. so your experiment is not good. >>> it's not that good, because the disk isn't fast. The swap test is the >>> workload with most significant impact I can get. >> >> Let me just interject here that a plug should be fine, from 3.1 we'll >> even auto-unplug if a certain depth has been reached. So latency should >> not be a worry. Personally I think the patch looks fine, though some >> numbers would be interesting to see. Cycles spent submitting the actual >> IO, combined with IO statistics what kind of IO patterns were observed >> for plain and with patch would be good. > I can observe the average request size changes. Before the patch, the > average request size is about 90k from iostat (but the variation is > big). With the patch, the request size is about 100k and variation is > small. That's a good win right there, imho. > how to check the cycles spend submitting the I/O? It's not easy, normal profiles is pretty much the only thing to go by. I guess I'm just a bit puzzled by Minchan's reluctance towards the patch, it seems like mostly goodness to me. -- Jens Axboe -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>