Messages in this thread | | | Date | Tue, 27 Jul 2004 11:03:38 -0700 | From | Hans Reiser <> | Subject | Re: clearing filesystem cache for I/O benchmarks |
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Benjamin Rutt wrote:
>Hans Reiser <reiser@namesys.com> writes: > > > >>when benchmarking, please be careful that you don't end up >>benchmarking umount/mount, or sync, or..... it can be remarkably hard >>to avoid such mistakes..... >> >> > >I agree, I've made some blunders like that in the past. However for >write tests, we are including fsync() time, once, at the end of a file >write, since I feel it's unfair to trim that time. > fsync performance gives you different performance. Better to write more stuff to flush the cache.
> Not including >fsync() time would only test the ability of the various parts of the >I/O systems to do write buffering. It's easy to do lots of write >buffering, if you buy enough memory. Forcing the disks to write is >the only fair way to compare writes between I/O systems. > > It isn't fair. fsync is a different code path, and may be less efficient. Or more, depending on the fs. reiser4 is currently not well optimized for fsync, maybe next year I will change that but not this week....
Benchmarking well is hard.....
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