Messages in this thread | | | From | Grant Coady <> | Subject | Re: Strange write starvation on 2.6.17 (and other) kernels | Date | Tue, 15 Aug 2006 09:28:58 +1000 |
| |
On Mon, 14 Aug 2006 18:36:44 +0200, Andrzej Szymanski <szymans@agh.edu.pl> wrote:
>Hi, > >I've encountered a strange problem - if an application is sequentially >writing a large file on a busy machine, a single write() of 64KB may >take even 30 seconds. But if I do fsync() after each write() the maximum >time of write()+fsync() is about 0.5 second (the overall performance is, >of course, degraded). > >The point is, that some applications (samba+smbclient) time out after >20s waiting for write(). > >Does anybody have an idea how to tune the kernel to avoid this strange >delay in write()? > >I've tried to experiment with cfq and deadline IO scheduler - without >success. Decreasing /proc/vm/dirty_ratio to 5% helps a little. > >If somebody want to test it, the tool I've written for measuring maximum >write() time is here: http://galaxy.agh.edu.pl/~szymans/writetimer > >1. Compile writetimer.c >2. Put a large background read from the disk >3. Simultaneously write 10 files 200MB each (write() without fsync()) >for i in 1 2 3 4 5 6 7 8 9 0 ; do ./writetimer 200 > testfile$i & done >4. and with fsync() after each write() >for i in 1 2 3 4 5 6 7 8 9 0 ; do ./writetimer -200 > testfile$i & done >(negative file size turns on fsync()) > >Tested on >- 2.6.15-23 (512MB RAM, Pentium-M 1.7, Ubuntu 6.06, ATA disk) >- 2.6.17-1.2145_FC5 (512MB RAM, Pentium-M 1.7, Fedora Core 5, ATA disk) >- 2.6.12-2.3.legacy_FC3smp (2GB RAM, Fedora Core 3, software RAID 5 on 4 >ATA disks)
Does top show what's holding up the file I/O? Rings a vague bell but I'm not able to run tests here for a little while until some other stuff completed.
Grant. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |