Re: Where is the performance bottleneck?

[jmerkey <jmerkey@utah-nac.org>]

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

Jeff


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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