On Thu, Apr 16, 2020 at 1:24 AM Mikulas Patocka <mpatocka@xxxxxxxxxx> wrote: > > > > 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? Maybe this is asking for a specific memcpy_flushcache_inatomic() implementation for your use case, but leave nt-writes for the general case? -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
