Re: Max IO size

[Mukul Kotwani <mkotwani@yahoo.com>]

Hello!
Thanks again!

If that is the case, then with my settings, is there
any other reason 512k requests are being broken down
into multiple 64k ones? 

Thanks!
Mukul

--- Jens Axboe <axboe@suse.de> wrote:
> On Thu, Aug 01 2002, Mukul Kotwani wrote:
> > 
> > Thanks for the reply!
> > 
> > All my values are set high. The sg_tablesize value
> is
> > set to 249, max_sectors set to 1024, and I dont
> think
> > there is any other value which affects IO size as
> > such. I didnt see anything called max segment
> size/max
> > size in the host template. Any other things I am
> > missing?
> 
> The max segment size is a property of the queue
> associated with the SCSI
> devices, it's in fact not directly controllable by
> the low level driver
> in the 2.4 kernels. What you can set in this regard
> is 'use_clustering'.
> With that set, the mid layer will attempt to merge
> contigious pages into
> the same scatter gather segment. This usually only
> provides a benefit
> with 1kb transfers (since they will typically be
> submitted in multiples
> anyway from the same page, thus it's easy to cluster
> them), with eg 4kb
> transfer sizes the amount of clustering that will
> happen is neglible.
> 
> -- 
> Jens Axboe
> 
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