From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bartlomiej Zolnierkiewicz Subject: Re: [PATCH 13/18] ide: use ->tf_load in SELECT_DRIVE() Date: Mon, 16 Feb 2009 22:51:49 +0100 Message-ID: <200902162251.49271.bzolnier@gmail.com> References: <20080620213323.13202.71450.sendpatchset@localhost.localdomain> <4998AE87.3020502@ru.mvista.com> <49995300.7030102@ru.mvista.com> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Return-path: Received: from fk-out-0910.google.com ([209.85.128.186]:13270 "EHLO fk-out-0910.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753805AbZBPVyF (ORCPT ); Mon, 16 Feb 2009 16:54:05 -0500 In-Reply-To: <49995300.7030102@ru.mvista.com> Content-Disposition: inline Sender: linux-ide-owner@vger.kernel.org List-Id: linux-ide@vger.kernel.org To: Sergei Shtylyov Cc: linux-ide@vger.kernel.org, linux-kernel@vger.kernel.org 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 > >>> 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...