Messages in this thread | | | Date | Wed, 31 Aug 2005 19:11:25 +0200 | From | Jens Axboe <> | Subject | Re: Where is the performance bottleneck? |
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On Wed, Aug 31 2005, jmerkey wrote: > > > I have seen an 80GB/sec limitation in the kernel unless this value is > changed in the SCSI I/O layer > for 3Ware and other controllers during testing of 2.6.X series kernels. > > Change these values in include/linux/blkdev.h and performance goes from > 80MB/S to over 670MB/S on the 3Ware controller. > > > //#define BLKDEV_MIN_RQ 4 > //#define BLKDEV_MAX_RQ 128 /* Default maximum */ > #define BLKDEV_MIN_RQ 4096 > #define BLKDEV_MAX_RQ 8192 /* Default maximum */
That's insane, you just wasted 1MiB of preallocated requests on each queue in the system!
Please just do
# echo 512 > /sys/block/dev/queue/nr_requests
after boot for each device you want to increase the queue size too. 512 should be enough with the 3ware.
-- Jens Axboe
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