From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1NAli8-0007zv-Tw for qemu-devel@nongnu.org; Wed, 18 Nov 2009 09:40:45 -0500 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1NAli4-0007vM-RD for qemu-devel@nongnu.org; Wed, 18 Nov 2009 09:40:44 -0500 Received: from [199.232.76.173] (port=32795 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1NAli4-0007uq-35 for qemu-devel@nongnu.org; Wed, 18 Nov 2009 09:40:40 -0500 Received: from mail-bw0-f212.google.com ([209.85.218.212]:37169) by monty-python.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1NAli3-0003KU-N4 for qemu-devel@nongnu.org; Wed, 18 Nov 2009 09:40:39 -0500 Received: by bwz4 with SMTP id 4so1425732bwz.2 for ; Wed, 18 Nov 2009 06:40:38 -0800 (PST) Date: Wed, 18 Nov 2009 16:41:22 +0200 From: Saul Tamari Message-ID: <20091118144122.GC19099@localhost.localdomain> References: <41be791c0911091004x62d30fbey91ef730475ba3571@mail.gmail.com> <4B02FBE4.2060409@codemonkey.ws> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline; filename="patch0.patch" In-Reply-To: <4B02FBE4.2060409@codemonkey.ws> Subject: [Qemu-devel] Re: [PATCH] qemu-kvm: clear only essential parts of VirtIOBlockReq on object allocation - RESUBMIT List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Anthony Liguori Cc: qemu-devel@nongnu.org, kvm@vger.kernel.org ok, Below is the patch. This time resent with mutt and hopefully without whitespace changes. -------------------------------------------------------------------- This patch reduces the amount of memory being cleared on every virtio-blk IO operation. 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; }