Re: Serious performance degradation on a RAID with kernel2.6.10-bk7 and later

[Nick Piggin]

On Wed, 2005-04-20 at 10:55 -0600, jmerkey wrote:
> 
> For 3Ware, you need to chage the queue depths, and you will see 
> dramatically improved performance. 3Ware can take requests
> a lot faster than Linux pushes them out. Try changing this instead, you 
> won't be going to sleep all the time waiting on the read/write
> request queues to get "unstarved".
> 
> 
> /linux/include/linux/blkdev.h
> 
> //#define BLKDEV_MIN_RQ 4
> //#define BLKDEV_MAX_RQ 128 /* Default maximum */
> #define BLKDEV_MIN_RQ 4096
> #define BLKDEV_MAX_RQ 8192 /* Default maximum */
> 

BTW, don't do this. BLKDEV_MIN_RQ sets the size of the mempool
reserved requests and will only get slightly used in low memory
conditions, so most memory will probably be wasted.

Just change /sys/block/xxx/queue/nr_requests

Nick



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