On Nov 18, 2010, at 3:07 PM, Ben Greear wrote: > I applied the NFS O_DIRECT patch (and all others) from the pending 2.6.36 stable > queue, and now I can at least use O_DIRECT w/out immediate failure. > > However, I notice that when writing 2k chunks with O_DIRECT on > NFS, it runs extremely slowly (about 300Kbps throughput). The > server is a Fedora 13 64-bit system running 2.6.34.7-56.fc13.x86_64 > > Here's some strace -ttT output for the writer: > > 07:03:42.898058 write(9, "\370'\37\345v\230\315\253\3\0\0\0\354\7\0\0\16\1\0\0\0\1\2\3\4\5\6\7\10\t\n\v"..., 2048) = 2048 <0.059402> > 07:03:42.957649 poll([{fd=4, events=POLLIN}, {fd=8, events=POLLIN}, {fd=6, events=POLLIN}], 3, 0) = 0 (Timeout) <0.000266> > 07:03:42.958148 write(9, "\212$s\327v\230\315\253\3\0\0\0\354\7\0\0\17\1\0\0\0\1\2\3\4\5\6\7\10\t\n\v"..., 2048) = 2048 <0.069295> > 07:03:43.027524 poll([{fd=4, events=POLLIN}, {fd=8, events=POLLIN}, {fd=6, events=POLLIN}], 3, 0) = 0 (Timeout) <0.000011> > > > Writing 64k chunks takes basically the same amount of time per system call: > > 07:06:13.537488 write(9, "\5\340\202\262v\230\315\253\3\0\0\0\354\377\0\0\6\0\0\0\0\1\2\3\4\5\6\7\10\t\n\v"..., 65536) = 65536 <0.049462> > 07:06:13.587083 poll([{fd=4, events=POLLIN}, {fd=8, events=POLLIN}, {fd=6, events=POLLIN}], 3, 0) = 0 (Timeout) <0.000035> > 07:06:13.587410 write(9, "\250\231\377cv\230\315\253\3\0\0\0\354\377\0\0\7\0\0\0\0\1\2\3\4\5\6\7\10\t\n\v"..., 65536) = 65536 <0.058612> > 07:06:13.646233 poll([{fd=4, events=POLLIN}, {fd=8, events=POLLIN}, {fd=6, events=POLLIN}], 3, 0) = 0 (Timeout) <0.000095> > 07:06:13.646616 write(9, "\5-@\5v\230\315\253\3\0\0\0\354\377\0\0\10\0\0\0\0\1\2\3\4\5\6\7\10\t\n\v"..., 65536) = 65536 <0.050282> > > > Reading is a good deal faster..about 34Mbps with O_DIRECT, NFS and 2k reads. > > Any ideas about why the write performance is so bad? A network trace will probably show you that the per-write latency is due to the server. -- Chuck Lever chuck[dot]lever[at]oracle[dot]com -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html