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Re: CVS commit: [tls-maxphys] src/sys/dev
On Tue, Oct 09, 2012 at 04:54:41PM -0400, Thor Lancelot Simon wrote:
> On Tue, Oct 09, 2012 at 10:15:06PM +0200, Manuel Bouyer wrote:
> > Now, iostat -x shows that sequential read of a large file (either with cat
> > or dd bs=1m) is done in 32k transfers at the disk level. So I guess
> > something
> > is not working properly here ...
> I saw that too, though I managed to get 64K transfers. I have been meaning
> to test with mmap, since that is more like the code path through the upper
> layers that produces the attempt to page in an entire executable.
> I've looked all through every layer I can identify and I do not see where
> the seemingly still remaining 64K restriction comes from. I thought it
> was FFS, but in fact *every vestige* of the maxcontig or "maximum extent
> size" use seems to have been excised from our FFS code. So it's a mystery
> to me.
There is still a reference to MAXPHYS in ufs_bmaparray(), which, if I got
it right, will limit the *runp in VOP_BMAP(), which will limit iobytes
but that doens't explain why I see 32k xfers. And, to make things worse,
I see 64k if I start the big file read with debug enabled, so it looks
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
NetBSD: 26 ans d'experience feront toujours la difference
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