Messages in this thread | | | Date | Fri, 27 Sep 2002 16:33:27 +0200 | From | Jens Axboe <> | Subject | Re: Warning - running *really* short on DMA buffers while doing file transfers |
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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
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