Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753883Ab2JVNGK (ORCPT ); Mon, 22 Oct 2012 09:06:10 -0400 Received: from mx1.redhat.com ([209.132.183.28]:18448 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753057Ab2JVNGI (ORCPT ); Mon, 22 Oct 2012 09:06:08 -0400 Date: Mon, 22 Oct 2012 15:05:58 +0200 From: Gleb Natapov To: Avi Kivity Cc: Jan Kiszka , Xiao Guangrong , Marcelo Tosatti , LKML , KVM Subject: Re: [PATCH] KVM: x86: fix vcpu->mmio_fragments overflow Message-ID: <20121022130558.GV29310@redhat.com> References: <20121022112314.GO29310@redhat.com> <50852F9C.9020808@siemens.com> <20121022114311.GQ29310@redhat.com> <508531E1.2030307@siemens.com> <508539A8.40404@redhat.com> <50853FF1.8010809@siemens.com> <20121022125301.GS29310@redhat.com> <5085423C.2020908@redhat.com> <20121022130102.GU29310@redhat.com> <508543DE.3080504@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <508543DE.3080504@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1058 Lines: 26 On Mon, Oct 22, 2012 at 03:02:22PM +0200, Avi Kivity wrote: > On 10/22/2012 03:01 PM, Gleb Natapov wrote: > > >> It's time where the guest cannot take interrupts, and time in a high > >> priority guest thread that is spent processing low guest priority requests. > >> > > Proposed fix has exactly same issue. Until all data is transfered to > > userspace no interrupt will be served. > > For mmio_fragments that is okay. It's the same guest instruction, and > it's still O(1). > > It's not okay for general mmio coalescing. > Ah, so optimizing mmio_fragments transmission to userspace using dedicated coalesced MMIO buffer should be fine then. Unfortunately, since we cannot use shared ring buffer that exists now, this is too much work for small gain that only new QEMU will be able to enjoy. -- Gleb. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/