Re: Warning - running *really* short on DMA buffers while doing file transfers

[Jens Axboe]

On Fri, Sep 27 2002, James Bottomley wrote:
> Therefore, it is in SCSI's interest to have the OS merge requests if it can 
> purely from the transport efficiency point of view.  Once we accept the 
> necessity of having the OS do some elevator work it becomes detrimental to 
> have this work repeated in the drive firmware.

Hear, hear. And given that the os io scheduler (I prefer to call it
that, elevator is pretty far from the truth :-) gets so close to drives
optimal performance in most cases, a small tag depth makes sense and
protects us from the latency concerns.

> I guess, however, that this issue will evaporate substantially once
> the aic7xxx driver uses ordered tags to represent the transaction
> integrity since the barriers will force the drive seek algorithm to
> follow the tag transmission order much more closely.

Depends on how often you issue these ordered tags, but yes I hope so
too.

-- 
Jens Axboe