On 05/04/2017 03:27 PM, Shaohua Li wrote: > On Thu, May 04, 2017 at 02:53:59PM -0600, Jens Axboe wrote: >> On 05/04/2017 02:42 PM, Shaohua Li wrote: >>> For fast flash disk, async IO could introduce overhead because of >>> context switch. block-mq now supports IO poll, which improves >>> performance and latency a lot. swapin is a good place to use this >>> technique, because the task is waitting for the swapin page to continue >>> execution. >> >> Nitfy! >> >>> In my virtual machine, directly read 4k data from a NVMe with iopoll is >>> about 60% better than that without poll. With iopoll support in swapin >>> patch, my microbenchmark (a task does random memory write) is about 10% >>> ~ 25% faster. CPU utilization increases a lot though, 2x and even 3x CPU >>> utilization. This will depend on disk speed though. While iopoll in >>> swapin isn't intended for all usage cases, it's a win for latency >>> sensistive workloads with high speed swap disk. block layer has knob to >>> control poll in runtime. If poll isn't enabled in block layer, there >>> should be no noticeable change in swapin. >> >> Did you try with hybrid polling enabled? We should be able to achieve >> most of the latency win at much less CPU cost with that. > > Hybrid poll is much slower than classic in my test, I tried different settings. > maybe because this is a vm though. It's probably a vm issue, I bet the timed sleep are just too slow to be useful in a vm. -- 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/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
