From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeff Garzik Subject: Re: [patch for 2.6.33? 1/1] ata: call flush_dcache_page() around PIO data transfers in libata-aff.c Date: Wed, 03 Feb 2010 12:15:46 -0500 Message-ID: <4B69AF42.5050508@pobox.com> References: <1265151518.2800.715.camel@mulgrave.site> <20100202150537.0f6a01c0.akpm@linux-foundation.org> <4B68B1E0.4090004@pobox.com> <20100202.152140.216335166.davem@davemloft.net> <1265153568.2800.815.camel@mulgrave.site> <1265192325.1970.28.camel@pc1117.cambridge.arm.com> <1265215254.2873.201.camel@mulgrave.site> <4B69ABCA.1030507@pobox.com> <20100203090631.44753f3b.akpm@linux-foundation.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from mail-yw0-f198.google.com ([209.85.211.198]:56756 "EHLO mail-yw0-f198.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932631Ab0BCRPt (ORCPT ); Wed, 3 Feb 2010 12:15:49 -0500 Received: by ywh36 with SMTP id 36so1466497ywh.15 for ; Wed, 03 Feb 2010 09:15:48 -0800 (PST) In-Reply-To: <20100203090631.44753f3b.akpm@linux-foundation.org> Sender: linux-ide-owner@vger.kernel.org List-Id: linux-ide@vger.kernel.org To: Andrew Morton Cc: James Bottomley , Catalin Marinas , David Miller , jeff@garzik.org, linux-ide@vger.kernel.org, stable@kernel.org, tj@kernel.org On 02/03/2010 12:06 PM, Andrew Morton wrote: > On Wed, 03 Feb 2010 12:00:58 -0500 Jeff Garzik wrote: > >> On 02/03/2010 11:40 AM, James Bottomley wrote: >>> The fix to libata looks to be just that it should kmap all the time >>> rather than trying to fiddle with the page to see if its higmem. For >>> kmap on a normal page, we should just return the offset map address and >>> do all the flushing. >> >> libata tests PageHighMem() because it was measurably faster to do things >> the current way (which includes local_irq_save/restore, only for >> highmem) on boxes where it actually matters. >> >> It seems more efficient to add a flush where necessary, than >> unconditionally punish everyone... > > kmap_atomic() tests PageHighMem() too - it's pretty lightweight for > lowmem pages. Note the lack of local_irq_save/restore in our code, though... These PIO xfers are __slow__, from the perspective of a CPU manufactured in the past decade; you are definitely disabling local interrupts for a long time. I suppose we could do if (high mem) local irq save kmap xfer kunmap local irq restore else kmap xfer kunmap does that solve the problem for ARM, for 2.6.33? > Anyway, I'd draw your attention to this claim in the changelog: "This > patch allows the ARM boards to use a rootfs on CompactFlash with the > PATA platform driver." Immediate-term, we should be looking for a small > fix for this issue which is acceptable for 2.6.33 and 2.6.32 and earlier. Sure... see above. hopefully one that does not punish -everybody- though. It would be sad to unconditionally slow down millions of volume platform (read: x86) users for some embedded boards. Jeff