Messages in this thread | | | From | Bartlomiej Zolnierkiewicz <> | Subject | Re: [PATCH 13/18] ide: use ->tf_load in SELECT_DRIVE() | Date | Mon, 16 Feb 2009 22:51:49 +0100 |
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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@gmail.com> > >>> 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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