From mboxrd@z Thu Jan 1 00:00:00 1970 From: Clay Haapala Subject: Re: PATCH: Further aacraid work Date: Thu, 17 Jun 2004 11:32:29 -0500 Sender: linux-scsi-owner@vger.kernel.org Message-ID: References: <547AF3BD0F3F0B4CBDC379BAC7E4189FD2402C@otce2k03.adaptec.com> <1087484107.2090.42.camel@mulgrave> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from rtp-iport-1.cisco.com ([64.102.122.148]:10606 "EHLO rtp-iport-1.cisco.com") by vger.kernel.org with ESMTP id S266563AbUFQQch (ORCPT ); Thu, 17 Jun 2004 12:32:37 -0400 In-Reply-To: <1087484107.2090.42.camel@mulgrave> (James Bottomley's message of "17 Jun 2004 09:55:03 -0500") List-Id: linux-scsi@vger.kernel.org To: James Bottomley Cc: "Salyzyn, Mark" , Christoph Hellwig , Alan Cox , Linux Kernel , SCSI Mailing List On 17 Jun 2004, James Bottomley spake thusly: > On Thu, 2004-06-17 at 09:39, Salyzyn, Mark wrote: >> This would not be such an issue if Linux provided large SG elements >> rather than the fubar descending page order ones they issue today. If >> this could be fixed, I'd not even be interested in the optimization of >> the SG. > > This is hardly a big problem, is it? it only occurs during the first > few moments of system operation. After that, the pages assigned to a > virtual region are pretty much random. > > Fundamentally, sg lists have to operate at the level of the MMU, so > we're stuck with the page size, which is 4k on x86. There's nothing we > can do in SCSI about this. > > Of course, if you're on a platform with an IOMMU then this problem > simply doesn't exist and we can coalesce nicely. > > James Just to see if my understanding is on track ... Today's scatterlists already handle entries with a size greater than MMU pagelength, even on x86, right? We have seen it in iSCSI driver testing, though it is not the usual case. crypto/digests.c:update() function was recently patched to handle the case and properly kmap() the additional memory represented by the sg entry. So, on regular x86 this is a matter of convenience/timing, and the page assignments will tend toward, but not always be, random 1-page entries as the system is used. -- Clay Haapala (chaapala@cisco.com) Cisco Systems SRBU +1 763-398-1056 6450 Wedgwood Rd, Suite 130 Maple Grove MN 55311 PGP: C89240AD Overheard somewhere in Washington D.C.: "Doh! Invaded the wrong country!"