From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:57287) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1W6ICz-0006RI-7Y for qemu-devel@nongnu.org; Thu, 23 Jan 2014 06:12:37 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1W6ICq-0001vZ-EW for qemu-devel@nongnu.org; Thu, 23 Jan 2014 06:12:29 -0500 Received: from e06smtp17.uk.ibm.com ([195.75.94.113]:33875) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1W6ICq-0001vO-6O for qemu-devel@nongnu.org; Thu, 23 Jan 2014 06:12:20 -0500 Received: from /spool/local by e06smtp17.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 23 Jan 2014 11:12:19 -0000 Received: from b06cxnps4076.portsmouth.uk.ibm.com (d06relay13.portsmouth.uk.ibm.com [9.149.109.198]) by d06dlp02.portsmouth.uk.ibm.com (Postfix) with ESMTP id 736B1219005C for ; Thu, 23 Jan 2014 11:12:15 +0000 (GMT) Received: from d06av01.portsmouth.uk.ibm.com (d06av01.portsmouth.uk.ibm.com [9.149.37.212]) by b06cxnps4076.portsmouth.uk.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id s0NBC5Kg57540608 for ; Thu, 23 Jan 2014 11:12:05 GMT Received: from d06av01.portsmouth.uk.ibm.com (localhost [127.0.0.1]) by d06av01.portsmouth.uk.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id s0NBCGA5009973 for ; Thu, 23 Jan 2014 04:12:16 -0700 Message-ID: <52E0F90F.6010701@de.ibm.com> Date: Thu, 23 Jan 2014 12:12:15 +0100 From: Christian Borntraeger MIME-Version: 1.0 References: <1389968119-24771-1-git-send-email-kwolf@redhat.com> <52E02A67.4060306@de.ibm.com> <20140123102930.GC8474@dhcp-200-207.str.redhat.com> In-Reply-To: <20140123102930.GC8474@dhcp-200-207.str.redhat.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH v3 00/29] block: Support for 512b-on-4k emulation List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Kevin Wolf Cc: pl@kamp.de, qemu-devel@nongnu.org, mreitz@redhat.com, stefanha@redhat.com, pbonzini@redhat.com, xiawenc@linux.vnet.ibm.com On 23/01/14 11:29, Kevin Wolf wrote: > Am 22.01.2014 um 21:30 hat Christian Borntraeger geschrieben: >> On 17/01/14 15:14, Kevin Wolf wrote: >>> This patch series adds code to the block layer that allows performing >>> I/O requests in smaller granularities than required by the host backend >>> (most importantly, O_DIRECT restrictions). It achieves this for reads >>> by rounding the request to host-side block boundary, and for writes by >>> performing a read-modify-write cycle (and serialising requests >>> touching the same block so that the RMW doesn't write back stale data). >> >> Nice, this might really help on s390 (also for KVM) since dasd disks usually >> have a 4k sector size. We also have flash systems with 4k block size. Both >> disk systems cause lots of trouble with cache=none and friends. > > Can't you configure guests to use 4k sector size as well? With these > patches, it should work, but there is an obvious performance penalty, so > you want the guest to make as little use of it as possible. Yes, thats what we do now, but it requires a command line parameter. A year ago or so we posted patches for block size detection (as well as geometry pass through) but the necessary rework after feedback is still pending (this got lost in a bunch of other todos, but we will restart that) > For PCs, it's essentially just the boot process that needs 512 byte > accesses because that's the BIOS interface, and the OS generally won't > send misaligned requests later. > > What's the situation on s390? Yes, its mostly the boot process. But there is also a problem if you have an image file on file system that is on a 4k disk. Then the guest might send non-aligned request IIRC. > >> Do you have a tree with these patches, so that I can test those on s390? > > Sure, and any testing is appreciated: > > git://repo.or.cz/qemu/kevin.git align > > Kevin >