lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
Open Source and information security mailing list archives
| ||
|
Date: Fri, 16 Apr 2010 14:27:58 +0200 From: Miklos Szeredi <mszeredi@...e.cz> To: Jens Axboe <jens.axboe@...cle.com> Cc: linux-kernel <linux-kernel@...r.kernel.org>, Jan Kara <jack@...e.cz>, Suresh Jayaraman <sjayaraman@...e.de> Subject: CFQ read performance regression Hi Jens, I'm chasing a performance bottleneck identified by tiobench that seems to be caused by CFQ. On a SLES10-SP3 kernel (2.6.16, with some patches moving cfq closer to 2.6.17) tiobench with 8 threads gets about 260MB/s sequential read throughput. On a recent kernels (including vanilla 2.6.34-rc) it makes about 145MB/s, a regression of 45%. The queue and readahead parameters are the same. This goes back some time, 2.6.27 already seems to have a bad performance. Changing the scheduler to noop will increase the throughput back into the 260MB/s range. So this is not a driver issue. Also increasing quantum *and* readahead will increase the throughput, but not by as much. Both noop and these tweaks decrease the write throughput somewhat however... Apparently on recent kernels the number of dispatched requests stays mostly at or below 4 and the dispatched sector count at or below 2000, which is not enough to fill the bandwidth on this setup. On 2.6.16 the number of dispatched requests hovers around 22 and the sector count around 16000. I uploaded blktraces for the read part of the tiobench runs for both 2.6.16 and 2.6.32: http://www.kernel.org/pub/linux/kernel/people/mszeredi/blktrace/ Do you have any idea about the cause of this regression? Thanks, Miklos -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists