From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:38759) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1T49ki-00027b-Bc for qemu-devel@nongnu.org; Wed, 22 Aug 2012 08:09:45 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1T49kh-0008IS-1i for qemu-devel@nongnu.org; Wed, 22 Aug 2012 08:09:40 -0400 Received: from mx1.redhat.com ([209.132.183.28]:31734) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1T49kg-0008IN-QD for qemu-devel@nongnu.org; Wed, 22 Aug 2012 08:09:38 -0400 Message-ID: <5034CBF8.3050602@redhat.com> Date: Wed, 22 Aug 2012 14:09:28 +0200 From: Paolo Bonzini MIME-Version: 1.0 References: <1345537427-21601-1-git-send-email-mc@linux.vnet.ibm.com> <50334B51.6050900@redhat.com> <503357B2.5040901@linux.vnet.ibm.com> <50335F78.1030005@redhat.com> <5034BCD1.9020603@linux.vnet.ibm.com> In-Reply-To: <5034BCD1.9020603@linux.vnet.ibm.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH 1/2 v1] blkdrv: Add queue limits parameters for sg block drive List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Cong Meng Cc: stefanha@linux.vnet.ibm.com, Stefan Hajnoczi , zwanp@cn.ibm.com, linuxram@us.ibm.com, qemu-devel@nongnu.org, virtualization@lists.linux-foundation.org Il 22/08/2012 13:04, Cong Meng ha scritto: >> >> Cong, what is the limit that the host HBA enforces (and what is the >> HBA)? What commands see a problem? Is it fixed by using scsi-block >> instead of scsi-generic (if you can use scsi-block at all, i.e. it's not >> a tape or similar device)? >> > I don't see real problem caused by the the queue limits actually. It's a > bug which Stefan told me. I'd rather avoid patching the specification if not to solve real (rather than known-but-theoretical) problems. >> With scsi-generic, QEMU uses a bounce buffer for non-I/O commands to a >> SCSI passthrough device, so the only problem in that case should be the >> maximum segment size. This could change in the future, but max_segments >> and max_sectors should not yet be a problem. > > about bounce buffer, do you meat the buffer allocated in > scsi_send_command() of hw/scsi-generic.c? Yes. Paolo