>-----Original Message----- >From: Jens Axboe [mailto:axboe@xxxxxx] >Sent: Thursday, May 04, 2017 2:29 PM >To: Shaohua Li >Cc: linux-mm@xxxxxxxxx; Andrew Morton; Kernel-team@xxxxxx; Chen, Tim C; >Huang, Ying >Subject: Re: [PATCH] swap: add block io poll in swapin path > >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. > The speedup is quite nice. The high CPU utilization is somewhat of a concern. But this is directly proportional to the poll time or latency of the drive's response. The latest generation of SSD drive's latency is a factor of 7 or more compared to the previous one, so the poll time could go down quite a bit, depending on what drive you were using in your test. What is the latency and the kind of drive you're using? Tim -- 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
