From mboxrd@z Thu Jan 1 00:00:00 1970 From: Saul Tamari Subject: [PATCH] qemu-kvm: clear only essential parts of VirtIOBlockReq on object allocation - RESUBMIT Date: Mon, 9 Nov 2009 20:04:34 +0200 Message-ID: <41be791c0911091004x62d30fbey91ef730475ba3571@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 To: qemu-devel@nongnu.org, kvm@vger.kernel.org Return-path: Received: from mail-ew0-f207.google.com ([209.85.219.207]:63019 "EHLO mail-ew0-f207.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752783AbZKISEf (ORCPT ); Mon, 9 Nov 2009 13:04:35 -0500 Received: by ewy3 with SMTP id 3so3380874ewy.37 for ; Mon, 09 Nov 2009 10:04:40 -0800 (PST) Sender: kvm-owner@vger.kernel.org List-ID: This patch reduces the size of memory being cleared on every virtio-blk IO. Improve number of IOPS when using avirtio-blk device. On every virtio-blk IO command passed to QEMU, virtio_blk_alloc_request() allocates and clears (with qemu_mallocz()) a VirtIOBlockReq object. The sizeof(VirtIOBlockReq) equals 41040 bytes on my x86-64 machine. By moving the 'elem' variable to the end of VirtIOBlockReq and clearing only upto the address of the 'elem.in_addr' field, the memset() call now clears only 80 bytes. Signed-off-by: Saul Tamari --- diff --git a/hw/virtio-blk.c b/hw/virtio-blk.c index 2630b99..de74b00 100644 --- a/hw/virtio-blk.c +++ b/hw/virtio-blk.c @@ -79,12 +79,13 @@ static inline void virtio_identify_template(struct virtio_blk_config *bc) typedef struct VirtIOBlockReq { VirtIOBlock *dev; - VirtQueueElement elem; struct virtio_blk_inhdr *in; struct virtio_blk_outhdr *out; struct virtio_scsi_inhdr *scsi; QEMUIOVector qiov; struct VirtIOBlockReq *next; + /* Members that need clearing, must be added prior to elem */ + VirtQueueElement elem; } VirtIOBlockReq; static void virtio_blk_req_complete(VirtIOBlockReq *req, int status) @@ -139,7 +140,8 @@ static void virtio_blk_flush_complete(void *opaque, int ret) static VirtIOBlockReq *virtio_blk_alloc_request(VirtIOBlock *s) { - VirtIOBlockReq *req = qemu_mallocz(sizeof(*req)); + VirtIOBlockReq *req = qemu_malloc(sizeof(*req)); + memset(req, 0, offsetof(VirtIOBlockReq, elem.in_addr[0])); req->dev = s; return req; }