From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gerd Hoffmann Subject: Re: [Qemu-devel] [RFC] Replace posix-aio with custom thread pool Date: Tue, 09 Dec 2008 16:51:57 +0100 Message-ID: <493E941D.4000608@redhat.com> References: <1228512061-25398-1-git-send-email-aliguori@us.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Anthony Liguori , kvm-devel To: qemu-devel@nongnu.org Return-path: Received: from mx2.redhat.com ([66.187.237.31]:54866 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751471AbYLIPwR (ORCPT ); Tue, 9 Dec 2008 10:52:17 -0500 In-Reply-To: <1228512061-25398-1-git-send-email-aliguori@us.ibm.com> Sender: kvm-owner@vger.kernel.org List-ID: Hi, > 2) it's impossible to add new interfaces and we need a vectored read/write > operation to properly support a zero-copy API. I'm eager to try vectored block ops for the xenbus block backend. > It performs at least as well as the current posix-aio code (in some > circumstances, even better). Well, I see a massive slowdown when switching from sync to aio in the xen backend code. I think the reason is that due to the lack of a vectored interface (and thus /me submitting separate aio requests for each iovec element) stuff gets parallelized *way* too much and disk seek times are killing me. > My only concern here is non-Linux Unices like FreeBSD. They have kernel support > for posix-aio. Since we cannot extend those interfaces though, I think that > even on those platforms we should still use a thread pool. Which might change some day in the future when we manage to get iovec support into posix-aio specs. I think the interface should use qemu-prefixed function and struct names. The we can trivially map them to a system-provided aio implementation without worrying about name clashes. cheers, Gerd