Simon Banton wrote: > > At 12:59 -0400 2/10/07, Ross S. W. Walker wrote: > >Try running the same benchmark but use bs=4k and count=1048576 > > Just finished doing that now - comparison graphs are here: > > http://community.novacaster.com/showarticle.pl?id=7492 > > >While these tests are running can you run any processes on another > >session? > > Yes, but responsiveness is sluggish eg (taken during 4k 'deadline' > scheduler test) > > # time ls /usr/lib > > real 0m15.959s > user 0m0.011s > sys 0m0.016s Well it looks like the CFQ actually was able to get some reads in while the background write was going on so it actually looks better in this workload scenario. I am going to retract my suggestion that 'deadline' be a general purpose scheduler for servers based on this. Instead I would make the following alternate suggestions. The issue I had with CFQ is it cannot handle overlapping IO well from multiple threads of the same process, so if your application does that (MySQL?) then it is probably NOT the right scheduler for you and you might be best to consider 'deadline' or 'noop' and put your data on a separate disk/array that doesn't compete with any other process/application. If an application spawns multiple threads or processes to handle completely separate data workloads (ie not overlapping io from same workload) then you are best using the default 'cfq' I believe. I would try some web benchmark app next with both cfq and then deadline to see which works better in a web-server environment. For web serving that is read only I suspect that either 'cfq' or 'deadline' will work well, but would like to know the results of your web benchmarks. In the end, since all your "content" will be in mysql and therefore all file system operations will be "read", the whole issue of being able to read while writing a large file isn't very relevant, so I would probably disregard it as an edge case that doesn't fit your workload. -Ross ______________________________________________________________________ This e-mail, and any attachments thereto, is intended only for use by the addressee(s) named herein and may contain legally privileged and/or confidential information. If you are not the intended recipient of this e-mail, you are hereby notified that any dissemination, distribution or copying of this e-mail, and any attachments thereto, is strictly prohibited. If you have received this e-mail in error, please immediately notify the sender and permanently delete the original and any copy or printout thereof.