Re: ide-cs using 100% CPU

Robert Hancock
2004-08-07T19:24:56Z

It isn't that the CPU is doing so much work, it's mostly waiting. However
with this type of PIO access, the CPU must do all the reads/writes from the
buffer and while doing this the CPU is blocked and cannot do anything else.

----- Original Message -----
From: "Hamie" <hamish@travellingkiwi.com>
Newsgroups: fa.linux.kernel
To: "Russell King" <rmk+lkml@arm.linux.org.uk>
Cc: <linux-kernel@vger.kernel.org>
Sent: Friday, August 06, 2004 1:46 PM
Subject: Re: ide-cs using 100% CPU

> Russell King wrote:
>
> >On Sun, Jul 18, 2004 at 10:30:16AM +0100, Hamie wrote:
> >
> >
> >>Anyone know why this happens? Something busy waiting? (BUt that should
> >>show as system cpu right?) or something taking out really long locks?
> >>
> >>
> >
> >It'll be because IDE is using PIO to access the CF card, which could
> >have long access times (so reading a block of sectors could take some
> >time _and_ use CPU.) Obviously, PIO requires the use of the CPU, so
> >the CPU can't be handed off to some other task while this is occuring.
> >
> >
> >
> Well... I did consider that. And not to disbelieve you, since you know
> the kernel way better than I do, But decided I was being silly that a
> 1.6GHz Pentium-M processor should use 100% CPU moving a couple of
> MB/second across a CF interface...
>
> Is 100% CPU not excessive? IIRC my PIII-750 used to use less CPU doing
> the same job as quick, or even slightly faster...
>
> And should it not use system CPU rather than user CPU?
>
> TIA
> Hamish.
>
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