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SubjectRe: Where is the performance bottleneck?

512 is not enough. It has to be larger. I just tried 512 and it still
limits the data rates.


Jens Axboe wrote:

>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.

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