On Thu, 9 Apr 2020, Mikulas Patocka wrote: > With dm-writecache on emulated pmem (with the memmap argument), we get > > With the original kernel: > 8508 - 11378 > real 0m4.960s > user 0m0.638s > sys 0m4.312s > > With dm-writecache hacked to use cached writes + clflushopt: > 8505 - 11378 > real 0m4.151s > user 0m0.560s > sys 0m3.582s I did some multithreaded tests: http://people.redhat.com/~mpatocka/testcases/pmem/microbenchmarks/pmem-multithreaded.txt And it turns out that for singlethreaded access, write+clwb performs better, while for multithreaded access, non-temporal stores perform better. 1 sequential write-nt 8 bytes 1.3 GB/s 2 sequential write-nt 8 bytes 2.5 GB/s 3 sequential write-nt 8 bytes 2.8 GB/s 4 sequential write-nt 8 bytes 2.8 GB/s 5 sequential write-nt 8 bytes 2.5 GB/s 1 sequential write 8 bytes + clwb 1.6 GB/s 2 sequential write 8 bytes + clwb 2.4 GB/s 3 sequential write 8 bytes + clwb 1.7 GB/s 4 sequential write 8 bytes + clwb 1.2 GB/s 5 sequential write 8 bytes + clwb 0.8 GB/s For one thread, we can see that write-nt 8 bytes has 1.3 GB/s and write 8+clwb has 1.6 GB/s, but for multiple threads, write-nt has better throughput. The dm-writecache target is singlethreaded (all the copying is done while holding the writecache lock), so it benefits from clwb. Should memcpy_flushcache be changed to write+clwb? Or are there some multithreaded users of memcpy_flushcache that would be hurt by this change? Mikulas -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
