Re: [SUGGESTION]: drop virtual merge accounting in I/O requests

[David Miller]

From: Andi Kleen <andi@xxxxxxxxxxxxxx>
Date: Sun, 13 Jul 2008 15:50:55 +0200

> Still I would expect that modern IO controllers are typically fast
> enough at processing SG lists that it shouldn't matter much.

I know it matters a lot on sparc64 ESP scsi controllers.

You can only have one address/len pair DMA'ing at a time and you have
to service an interrupt to load in the the next DMA sg elements into
the chips registers.

Merging is essentially a must for performance on those cards.
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