On Thu, Oct 29, 2020 at 07:57:34AM -0600, Jens Axboe wrote: > On 10/28/20 4:26 PM, Jens Axboe wrote: > > I did see some wins when I tested this. I'll try and run some testing > > tomorrow and report back. If there's something specifically you want to > > see tested, let me know. > > I did some testing, unfortunately it's _very_ hard to produce somewhat > consistent and good numbers as it quickly becomes a game of kswapd. > Here's a basic case of 4 threads doing 32k random reads: > > PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND > 462 root 20 0 0 0 0 R 65.5 0.0 0:08.02 kswapd0 > 2287 axboe 20 0 1303448 2176 1072 R 46.6 0.0 0:05.35 fio > 2289 axboe 20 0 1303456 2196 1092 D 46.6 0.0 0:05.34 fio > 2290 axboe 20 0 1303460 2216 1112 D 46.6 0.0 0:05.37 fio > 2288 axboe 20 0 1303452 2224 1120 R 45.9 0.0 0:05.33 fio > > Sad face... Unfortunately once kswapd kicks in, performance also > plummets. This box only has 32G of ram, and you can fill that in less > than 10 seconds doing buffered reads like that. > > I ran 4k and 32k testing, and using 1 and 4 threads. But given the above > sadness, it quickly ends up looking the same for me. What if your workload actually fits in memory? That would seem to be the situation where Kent's patches would make a difference.
