Jeff V. Merkey wrote: > Jens Axboe wrote: > >On Mon, Jan 16 2006, Jeff V. Merkey wrote: > >>Max Waterman wrote: > >>>I've noticed that I consistently get better (read) numbers from kernel > >>>2.6.8 than from later kernels. > >> > >>To open the bottlenecks, the following works well. Jens will shoot me > >>-#define BLKDEV_MIN_RQ 4 > >>-#define BLKDEV_MAX_RQ 128 /* Default maximum */ > >>+#define BLKDEV_MIN_RQ 4096 > >>+#define BLKDEV_MAX_RQ 8192 /* Default maximum */ > > > >Yeah I could shoot you. However I'm more interested in why this is > >necessary, eg I'd like to see some numbers from you comparing: > > > >- Doing > > # echo 8192 > /sys/block/<dev>/queue/nr_requests > > for each drive you are accessing. > > > >The BLKDEV_MIN_RQ increase is just silly and wastes a huge amount of > >memory for no good reason. > > Yep. I build it into the kernel to save the trouble of sending it to proc. > Jens recommendation will work just fine. It has the same affect of > increasing the max requests outstanding. Your suggestion doesn't do anything here on 2.6.15, but echo 192 > /sys/block/<dev>/queue/max_sectors_kb echo 192 > /sys/block/<dev>/queue/read_ahead_kb works wonders! I don't know why, but anything less than 64 and more than 256 makes the queue collapse miserably, causing some strange __copy_to_user calls?!?!? Also, it seems that changing the kernel HZ has some drastic effects on the queues. A simple lilo gets delayed 400% and 200% using 100HZ and 250HZ respectively. -- Al - 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
