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

[Tejun Heo <tj@home-tj.org>]

Hello,

Bartlomiej Zolnierkiewicz wrote:
> On Wed, 2 Feb 2005 12:06:03 +0900, Tejun Heo <tj@home-tj.org> 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@home-tj.org>
> 
> 
> 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