2017-04-01 13:37 GMT+08:00 Fam Zheng <f...@redhat.com>: > 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
Modifying libnfs is also a solution. However, when I looked into libnfs, found that it is totally single-thread design. It would be a lot work to make it support multi-thread mode. That is why I choose to modify qemu block/nfs.c instead. Because there are already some similar ways like file-posix.c. -- Best regards, Jaden Liang
