Re: [PATCH 2.6.11-rc2 21/29] ide: Merge do_rw_taskfile() and flagged_taskfile().

[Tejun Heo]

Hello,

Bartlomiej Zolnierkiewicz wrote:
> On Wed, 2 Feb 2005 12:06:03 +0900, Tejun Heo <tj@xxxxxxxxxxx> wrote:
>
> > > 21_ide_do_taskfile.patch
> > >
> > >      Merged do_rw_taskfile() and flagged_taskfile() into
> > >      do_taskfile().  During the merge, the following changes took
> > >      place.
> > >      1. flagged taskfile now honors HOB feature register.
> > >         (do_rw_taskfile() did write to HOB feature.)
> > >      2. No do_rw_taskfile() HIHI check on select register.  Except
> > >         for the DEV bit, all bits are honored.
> > >      3. Uses taskfile->data_phase to determine if dma trasfer is
> > >         requested.  (do_rw_taskfile() directly switched on
> > >         taskfile->command for all dma commands)
> >
> > Signed-off-by: Tejun Heo <tj@xxxxxxxxxxx>
>
>
> do_rw_taskfile() is going to be used by fs requests once
> __ide_do_rw_disk() is converted to taskfile transport.
>
> I don't think that do_rw_taskfile() and flagged_taskfile() merge
> is a good thing as it adds unnecessary overhead for hot path
> (fs requests).

Yeah, I also thought about that, but here are reasons why I still think 
merging is better.

1. The added overhead is small.  It's just a dozen more if's per every 
disk io.  I don't think it will make any noticeable difference.

2. If hot path optimization is needed, it can be easily done inside one 
do_taskfile() function with one or two more if's.

3. Currently, do_rw_taskfile() isn't used by __ide_do_rw_disk().  We can 
think about optimization when actually converting it to use taskfile 
transport.  And IMHO, if hot path optimization is needed, leaving hot 
path optimization where it is now (inside __ide_do_rw_disk()) is better 
 than moving it to separate taskfile function (do_rw_taskfile()).

--
tejun

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