From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1L6Vnm-0001wl-Fq for qemu-devel@nongnu.org; Sat, 29 Nov 2008 14:48:26 -0500 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1L6Vnk-0001w0-MX for qemu-devel@nongnu.org; Sat, 29 Nov 2008 14:48:25 -0500 Received: from [199.232.76.173] (port=42122 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1L6Vnk-0001vp-E3 for qemu-devel@nongnu.org; Sat, 29 Nov 2008 14:48:24 -0500 Received: from mx2.redhat.com ([66.187.237.31]:47418) by monty-python.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1L6Vnj-0008Ln-D0 for qemu-devel@nongnu.org; Sat, 29 Nov 2008 14:48:24 -0500 Received: from int-mx2.corp.redhat.com (int-mx2.corp.redhat.com [172.16.27.26]) by mx2.redhat.com (8.13.8/8.13.8) with ESMTP id mATJmL3G015893 for ; Sat, 29 Nov 2008 14:48:21 -0500 Message-ID: <49319C86.8050408@redhat.com> Date: Sat, 29 Nov 2008 21:48:22 +0200 From: Avi Kivity MIME-Version: 1.0 Subject: Re: [Qemu-devel] [RFC 1/2] pci-dma-api-v1 References: <20081127123538.GC10348@random.random> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Reply-To: qemu-devel@nongnu.org List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Blue Swirl wrote: > The previous similar attempt by Anthony for generic DMA using vectored > IO was abandoned because the malloc/free overhead was more than the > performance gain. Have you made any performance measurements? How does > this version compare to the previous ones? > > The pointers you gave don't blame malloc/free, instead the lack of aio readv/writev. Since Andrea's patches contain emulation for aio readv/writev, the performance degradation will not occur (though we will not see the benefit either). I doubt you can get measure malloc overhead with anything less a thousand disks (even there, other overheads are likely to drown that malloc). -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.