From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:35273) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1VBhTt-0004gA-Q1 for qemu-devel@nongnu.org; Tue, 20 Aug 2013 04:40:07 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1VBhTn-0004DY-ES for qemu-devel@nongnu.org; Tue, 20 Aug 2013 04:40:01 -0400 Message-ID: <52132B28.9030803@redhat.com> Date: Tue, 20 Aug 2013 10:39:04 +0200 From: Paolo Bonzini MIME-Version: 1.0 References: <1375862885-12132-1-git-send-email-aik@ozlabs.ru> <520DF5B5.4050805@ozlabs.ru> <5210E6C2.1070208@redhat.com> <5211C99B.4070904@ozlabs.ru> <0E406847-EB38-4E35-9447-657BFF7FF70A@suse.de> <5211DAD3.1050602@ozlabs.ru> <5211E9AB.7050700@redhat.com> <5212C81B.2090403@ozlabs.ru> In-Reply-To: <5212C81B.2090403@ozlabs.ru> Content-Type: text/plain; charset=KOI8-R Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] powerpc iommu: enable multiple TCE requests List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Alexey Kardashevskiy Cc: Alexander Graf , "qemu-devel@nongnu.org" , "qemu-ppc@nongnu.org" , Paul Mackerras , David Gibson Il 20/08/2013 03:36, Alexey Kardashevskiy ha scritto: > Hm. Here we might have a problem like this is we decide to migrate from > QEMU with this patch running on modern kernel to QEMU without this patch > running on old kernel - for this we might want to be able to disable > "multi-tce" via machine options on newer kernels. Do we care enough to add > such a parameter or we just disable migration and that's it? Upstream doesn't support migration to older QEMU. > This SandyBridge,enforce - what if the destination host running on old > kernel was run without this option - will the migration fail? The destination machine will not even start. >> But in this case, you do not need this because the hypercall works if >> emulated by QEMU. I like Alex's solution of making it universally >> available in the dtb. > > The solution would be good if we did not already have H_PUT_TCE accelerated > for emulated devices in the host kernel but we do have it. The question is also whether you consider pSeries support complete enough to be production ready---and until you have versioned machine types I would say you don't. If you still consider it somewhat experimental, I would do as Alex said: make newer QEMU on older KVM as slower, and that's it. Paolo