Re: [PATCH] ide: add dcache flushing after PIO

[Russell King <rmk@arm.linux.org.uk>]

On Sat, Jan 07, 2006 at 09:17:11PM +0100, Bartlomiej Zolnierkiewicz wrote:
> On 1/7/06, Russell King <rmk@arm.linux.org.uk> wrote:
> > On Wed, Dec 21, 2005 at 05:54:16PM +0000, Russell King wrote:
> > > DaveM vetoed that with good reason - the VM layer doesn't know whether
> > > the driver is doing PIO or not.  If it is doing PIO, it needs the
> > > cache flush.  If it's doing DMA, the cache flush is entirely a
> > > performance bottleneck.
> >
> > Bart,
> >
> > Did you miss my message, or have you decided to pay no further
> > attention to this issue?
> 
> No, I'm waiting for ARM folks to give Tejun and me some feedback.

We have, and I think it's been soo long that you're now confused.
See the entire thread on marc:

http://marc.theaimsgroup.com/?t=113517374400003&r=1&w=2

Yes, Tejun produced a patch and I queried whether it was going to
far.  There was a bit of discussion which resulted in a comment from
you saying:

| After reading excellent explanation by rmk I think that it should be
| fixed at VM layer (filemap_nopage() perhaps).

To which I replied:

| DaveM vetoed that with good reason - the VM layer doesn't know whether
| the driver is doing PIO or not.  If it is doing PIO, it needs the
| cache flush.  If it's doing DMA, the cache flush is entirely a
| performance bottleneck.

That's where we stand now - I'm waiting for some progress.

> So far there was none and nobody seemed to care to test/comment
> this patch ("works fine" is enough).

Odd, as demonstrated by the linux-ide archives above I've already
commented on it.

> What about testing the patch instead?

Since there hasn't been a follow-up patch, there isn't anything to
test.  Please can we have a revised patch so folk _can_ do some
testing?

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:  2.6 Serial core