Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932380AbbFQNPP (ORCPT ); Wed, 17 Jun 2015 09:15:15 -0400 Received: from mx1.redhat.com ([209.132.183.28]:59257 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932328AbbFQNPK (ORCPT ); Wed, 17 Jun 2015 09:15:10 -0400 From: Igor Mammedov To: linux-kernel@vger.kernel.org Cc: mst@redhat.com, kvm@vger.kernel.org, pbonzini@redhat.com, andrey@xdel.ru, digitaleric@google.com Subject: [PATCH v2 4/6] vhost: translate_desc: optimization for desc.len < region size Date: Wed, 17 Jun 2015 15:14:57 +0200 Message-Id: <1434546899-5296-5-git-send-email-imammedo@redhat.com> In-Reply-To: <1434546899-5296-1-git-send-email-imammedo@redhat.com> References: <1434546899-5296-1-git-send-email-imammedo@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2047 Lines: 73 when translating descriptors they are typically less than memory region that holds them and translated into 1 iov entry, so it's not nessesary to check remaining length twice and calculate used length and next address in such cases. replace a remaining length and 'size' increment branches with a single remaining length check and execute next iov steps only when it needed. It saves a tiny 2% of translate_desc() execution time. Signed-off-by: Igor Mammedov --- PS: I'm not sure if iov_size > 0 is always true, if it's not then better to drop this patch. --- drivers/vhost/vhost.c | 21 +++++++++++++-------- 1 file changed, 13 insertions(+), 8 deletions(-) diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c index 5c39a1e..5bcb323 100644 --- a/drivers/vhost/vhost.c +++ b/drivers/vhost/vhost.c @@ -1111,12 +1111,8 @@ static int translate_desc(struct vhost_virtqueue *vq, u64 addr, u32 len, int ret = 0; mem = vq->memory; - while ((u64)len > s) { + do { u64 size; - if (unlikely(ret >= iov_size)) { - ret = -ENOBUFS; - break; - } reg = find_region(mem, addr, len, &vq->cached_reg); if (unlikely(!reg)) { ret = -EFAULT; @@ -1124,13 +1120,22 @@ static int translate_desc(struct vhost_virtqueue *vq, u64 addr, u32 len, } _iov = iov + ret; size = reg->memory_size - addr + reg->guest_phys_addr; - _iov->iov_len = min((u64)len - s, size); _iov->iov_base = (void __user *)(unsigned long) (reg->userspace_addr + addr - reg->guest_phys_addr); + ++ret; + if (likely((u64)len - s < size)) { + _iov->iov_len = (u64)len - s; + break; + } + + if (unlikely(ret >= iov_size)) { + ret = -ENOBUFS; + break; + } + _iov->iov_len = size; s += size; addr += size; - ++ret; - } + } while (1); return ret; } -- 1.8.3.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/