From mboxrd@z Thu Jan 1 00:00:00 1970 From: Anthony Liguori Subject: Re: [PATCH 03/21] Remove use of signalfd in block-raw-posix.c Date: Thu, 30 Apr 2009 08:28:38 -0500 Message-ID: <49F9A786.5020306@us.ibm.com> References: <1241040038-17183-1-git-send-email-aliguori@us.ibm.com> <1241040038-17183-4-git-send-email-aliguori@us.ibm.com> <49F96F37.2070002@redhat.com> <49F99F8A.8010806@codemonkey.ws> <49F9A1FC.2060705@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org To: Avi Kivity Return-path: Received: from e33.co.us.ibm.com ([32.97.110.151]:32960 "EHLO e33.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756394AbZD3N2v (ORCPT ); Thu, 30 Apr 2009 09:28:51 -0400 Received: from d03relay02.boulder.ibm.com (d03relay02.boulder.ibm.com [9.17.195.227]) by e33.co.us.ibm.com (8.13.1/8.13.1) with ESMTP id n3UDR9mZ003706 for ; Thu, 30 Apr 2009 07:27:09 -0600 Received: from d03av03.boulder.ibm.com (d03av03.boulder.ibm.com [9.17.195.169]) by d03relay02.boulder.ibm.com (8.13.8/8.13.8/NCO v9.2) with ESMTP id n3UDSpPd256784 for ; Thu, 30 Apr 2009 07:28:51 -0600 Received: from d03av03.boulder.ibm.com (loopback [127.0.0.1]) by d03av03.boulder.ibm.com (8.12.11.20060308/8.13.3) with ESMTP id n3UDSnQ2001356 for ; Thu, 30 Apr 2009 07:28:51 -0600 In-Reply-To: <49F9A1FC.2060705@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: Avi Kivity wrote: > Anthony Liguori wrote: >> Avi Kivity wrote: >>> Anthony Liguori wrote: >>>> We don't use signalfd in upstream QEMU. Instead, we always emulate >>>> it. >>>> >>> >>> With an extra thread -> so an extra context switch. >> >> We don't use an extra thread. We just install a signal handler that >> writes to a pipe. At best, the added overhead is that we get EINTRs >> more often but this is something we already handle. > > Oh okay. But signal delivery is slow; for example the FPU needs to be > reset. Is it really justified to add all of this extra code (including signalfd emulation) for something that probably isn't even measurable? I like using wiz-bang features of Linux as much as the next guy, but I think we're stretching to justify it here :-) -- Regards, Anthony Liguori