On Monday 16 February 2009, Sergei Shtylyov wrote:
> Hello, I wrote:
>
> >>> There should be no functional changes caused by this patch.
> >>> Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@xxxxxxxxx>
> >>> Index: b/drivers/ide/ide-iops.c
> >>> ===================================================================
> >>> --- a/drivers/ide/ide-iops.c
> >>> +++ b/drivers/ide/ide-iops.c
> >>> @@ -88,11 +88,15 @@ void SELECT_DRIVE (ide_drive_t *drive)
> >>> {
> >>> ide_hwif_t *hwif = drive->hwif;
> >>> const struct ide_port_ops *port_ops = hwif->port_ops;
> >>> + ide_task_t task;
> >>>
> >>> if (port_ops && port_ops->selectproc)
> >>> port_ops->selectproc(drive);
> >>>
> >>> - hwif->OUTB(drive->select.all, hwif->io_ports.device_addr);
> >>> + memset(&task, 0, sizeof(task));
> >>> + task.tf_flags = IDE_TFLAG_OUT_DEVICE;
> >>> +
> >>> + drive->hwif->tf_load(drive, &task);
> >>
> >> This actually doesn't seem like a bright idea to me, considering
> >> that this gets called when starting every request. How will you look
> >> at me adding the transport method for writing this register? :-)
Please check profiles first -- it might not be worth it. [1]
> > Convert SELECT_DRIVE() to use ->tf_load instead of ->OUTB.
> >
> > OTOH, adding such a "backdoor" to the taskfile doesn't seem very
> > consistent... well, I'm not excited about the whole idea conversion to
> > tf_{load|read}() -- it's not clear what exactly this bought us.
This was explained some months ago already, so just to recall -- it was
a part of a bigger work removing duplicated code and allowing abstraction
of the ATA logic.
Anyway this is not set in a stone so if you have proposal of a better
approach please come forward with it.
> We at least could have saved on memset() -- tf_load() method ignores
> fields other than tf_flags anyway...
Unless it is huge performance win (unlikely) this is not a good idea
as it would be a maintainance nightmare.
->tf_load does only use cmd->tf_flags today but it might change one day
and nobody will remember to audit all users that they pass a valid cmd...
Thanks,
Bart
[1] coincidentally on the past Saturday I woke up with a bright idea
of doing some profiling of IDE code... I thought this would be a fun...
# readprofile -m System.map | grep ide_
30 ide_intr 0.0714
1 ide_map_sg 0.0112
1 ide_complete_rq 0.0152
78 do_ide_request 0.0643
1 __ide_wait_stat 0.0059
51 ide_execute_command 0.5100
4 ide_set_handler 0.0635
7 ide_outb 1.1667
308 ide_mm_inb 44.0000
...
This was on ICH4 PATA controller... Fun indeed, ain't it?
[ For non-ATA folks: it is _impossible_ for ide_mm_inb to be used
on the above controller. ]
I still have to check what will happen if I would change the order
of following assignments in ide_tf_read():
...
if (mmio) {
tf_outb = ide_mm_outb;
tf_inb = ide_mm_inb;
} else {
tf_outb = ide_outb;
tf_inb = ide_inb;
}
...
However I instead I went ahead and tried to run oprofile to get me some
more trushworthy results:
# opreport -l vmlinux
CPU: Pentium M (P6 core), speed 600 MHz (estimated)
Counted CPU_CLK_UNHALTED events (clocks processor is not halted, and not in a thermal trip) with a unit mask of 0x00 (No unit mask) count 100000
Segmentation fault
After this, testing some older kernel versions and assuring that user-space
packages are at their latest distro versions I had enough of fun...
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