On Mon, 15 Oct 2007, Bernd Schubert wrote:
Hi, in order to tune raid performance I did some benchmarks with and without the stripe queue patches. 2.6.22 is only for comparison to rule out other effects, e.g. the new scheduler, etc. It seems there is a regression with these patch regarding the re-write performance, as you can see its almost 50% of what it should be. write re-write read re-read 480844.26 448723.48 707927.55 706075.02 (2.6.22 w/o SQ patches) 487069.47 232574.30 709038.28 707595.09 (2.6.23 with SQ patches) 469865.75 438649.88 711211.92 703229.00 (2.6.23 without SQ patches) Benchmark details: 3xraid5 over 4 partitions of the very same hardware raid (in the end thats raid65, raid6 in hardware and raid5 in software, we need to do that). chunk size: 8192 stripe_cache_size: 8192 each readahead of the md*: 65535 (well actually it limits itself to 65528 readahead of the underlying partitions: 16384 filesystem: xfs Testsystem: 2 x Quadcore Xeon 1.86 GHz (E5320) An interesting effect to notice: Without these patches the pdflush daemons will take a lot of CPU time, with these patches, pdflush almost doesn't appear in the 'top' list. Actually we would prefer one single raid5 array, but then one single raid5 thread will run with 100% CPU time leaving 7 CPUs idle state, the status of the hardware raid says its utilization is only at about 50% and we only see writes at about 200 MB/s. On the contrary, with 3 different software raid5 sets the i/o to the harware raid systems is the bottleneck. Is there any chance to parallize the raid5 code? I think almost everything is done in raid5.c make_request(), but the main loop there is spin_locked by prepare_to_wait(). Would it be possible not to lock this entire loop? Thanks, Bernd -- Bernd Schubert Q-Leap Networks GmbH - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
Excellent questions I look forward to reading this thread :) Justin. - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
