Re: [Kiobuf-io-devel] RFC: Kernel mechanism: Compound event wait

[Richard Gooch]

Stephen C. Tweedie writes:
> Hi,
> 
> On Tue, Feb 06, 2001 at 06:37:41PM -0800, Linus Torvalds wrote:
> > Absolutely. And this is independent of what kind of interface we end up
> > using, whether it be kiobuf of just plain "struct buffer_head". In that
> > respect they are equivalent.
> 
> Sorry?  I'm not sure where communication is breaking down here, but
> we really don't seem to be talking about the same things.  SGI's
> kiobuf request patches already let us pass a large IO through the
> request layer in a single unit without having to split it up to
> squeeze it through the API.

Isn't Linus saying that you can use (say) 4 kiB buffer_heads, so you
don't need kiobufs? IIRC, kiobufs are page containers, so a 4 kiB
buffer_head is effectively the same thing.

> If you really don't mind the size of the buffer_head as a sg fragment
> header, then at least I'd like us to be able to submit a pre-built
> chain of bh's all at once without having to go through the remap/merge
> cost for each single bh.

Even if you are limited to feeding one buffer_head at a time, the
merge costs should be somewhat mitigated, since you'll decrease your
calls into the API by a factor of 8 or 16.
But an API extension to allow passing a pre-built chain would be even
better.

Hopefully I haven't missed the point. I've got the flu so I'm not
running on all 4 cylinders :-(

                                Regards,

                                        Richard....
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