On Sat, 04/01 13:23, Jaden Liang wrote: > Hello, > > I ran qemu with drive file via libnfs recently, and found some performance > problem and an improvement idea. > > I started qemu with 6 drives parameter like > nfs://127.0.0.1/dir/vm-disk-x.qcow2 > which linked to a local NFS server, then used iometer in guest machine to test > the 4K random read or random write IO performance. I found that while the IO > depth go up, the IOPS hit a bottleneck. I looked into the causes, found that > the > main thread of qemu used 100% CPU. From the perf data, it show the CPU heats > are > send / recv calls in libnfs. By reading the source code of libnfs and qemu > block > drive of nfs.c, libnfs only support single work thread, and the network events > of nfs interface in qemu are all registered in the epoll of main thread. That > is > the cause why main thread uses 100% CPU. > > After the analysis above, there is an improvement idea comes up. I start a > thread for every drive while libnfs open drive file, then create an epoll in > every drive thread to handle all of the network events. I have finished an > demo > modification in block/nfs.c, then rerun iometer in the guest machine, the > performance increased a lot. Random read IOPS increases almost 100%, random > write IOPS increases about 68%. > > Test model details > VM configure: 6 vdisks in 1 VM > Test tool and parameter: iometer with 4K random read and randwrite > Backend physical drive: 2 SSDs, 6 vdisks are seperated in 2 SSDs > > Before modified: > IO Depth 1 2 4 8 16 32 > 4K randread 16659 28387 42932 46868 52108 55760 > 4K randwrite 12212 19456 30447 30574 35788 39015 > > After modified: > IO Depth 1 2 4 8 16 32 > 4K randread 17661 33115 57138 82016 99369 109410 > 4K randwrite 12669 21492 36017 51532 61475 65577 > > I could put a up to coding standard patch later. Now I want to get some advise > about this modification. Is this a reasonable solution to improve performance > in > NFS shares? Or there is another better way? > > Any suggestions would be great! Also please feel free to ask question.
Just one comment: in block/file-posix.c (aio=threads), there is a thread pool that does something similar, using the code util/thread-pool.c. Maybe it's usable for your block/nfs.c change too. Also a question: have you considered modifying libnfs to create more worker threads? That way all applications using libnfs can benefit. Fam
