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. Thanks, Shaohua -- 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>
