Re: I/O very slow under 2.4 (device reading)

[Linus Torvalds]

In article <[e-mail]>,
 <[e-mail] ( Marc) (A.) (Lehmann )> wrote:
>It might be vm related, it might be not, but I get very funny effects when
>running:
>
>   buffer -S1m -s128k -m32m </dev/hde >/dev/null
>
>(buffer is just a fast read/write buffer reading stdin to stdout, i use it
>to check wether all sectors of a disk are readable, it's similar to dd,
>which creates the same effects).

I bet it's the same thing that made writes slow - the buffer allocator
and the VM disagree about how/when to allocate memory. It's fixed by the patch
that's floating around in the "VM suckage" thread along with the tweak
to fix "zone_free_plenty()".

I'll make a real pre-patch (2.4.8-pre7) with the full changeset, can you
test that out? I did an equivalent "dd" that you see problems with, and
on my current kernel as long as there isn't other IO activity it stays
at a nice stable 21MB/s which is all my disk can deliver. 

[ Damn, maybe I should get one of those nice big 7200 rpm IBM drives ]

		Linus