Erez Zilber wrote:
> On Tue, Feb 17, 2009 at 11:35 PM, Mike Christie <micha...@cs.wisc.edu> wrote:
>> Erez Zilber wrote:
>>> Hi,
>>>
>>> I'm running a setup of open-iscsi connected to a target. When I run
>>> I/O from the initiator (e.g using dd) with transaction size of 128kB,
>>> I sometimes see that 2 128kB requests are aggregated to a single 256kB
>>> request. This is rare, but it happens from time to time. Can I disable
>>> this feature? Who is responsible for that? Is it scsi-ml?
>>>
>> block layer.
>>
>> /sys/block/sdX/queue/max_sectors_kb
> 
> Thanks, but this will limit the I/O size for all I/Os. What I forgot
> to mention is that sometimes I also send larger I/Os (e.g. 512kB).
> With the proposed solution, these large I/Os will be sent as multiple
> 128kB I/Os (and affect the performance). Isn't there a way to simply
> avoid this aggregation?
> 

Not that I know of when going through the block layer. I think you will 
have to ask lkml.

I think the only way to control it is the  bsg/sg/passthrough route 
since that does not do merging. The other alternative is to just hack 
the code to do what you want :)

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