From patchwork Sun Mar 13 15:06:47 2011 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Michael S. Tsirkin" X-Patchwork-Id: 86600 X-Patchwork-Delegate: davem@davemloft.net Return-Path: X-Original-To: patchwork-incoming@ozlabs.org Delivered-To: patchwork-incoming@ozlabs.org Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by ozlabs.org (Postfix) with ESMTP id 5179AB6F7C for ; Mon, 14 Mar 2011 02:07:52 +1100 (EST) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753022Ab1CMPHZ (ORCPT ); Sun, 13 Mar 2011 11:07:25 -0400 Received: from mx1.redhat.com ([209.132.183.28]:22938 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753103Ab1CMPHA (ORCPT ); Sun, 13 Mar 2011 11:07:00 -0400 Received: from int-mx10.intmail.prod.int.phx2.redhat.com (int-mx10.intmail.prod.int.phx2.redhat.com [10.5.11.23]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id p2DF6viI027777 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK); Sun, 13 Mar 2011 11:06:57 -0400 Received: from redhat.com (vpn-200-105.tlv.redhat.com [10.35.200.105]) by int-mx10.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with SMTP id p2DF6sfS029614; Sun, 13 Mar 2011 11:06:55 -0400 Date: Sun, 13 Mar 2011 17:06:47 +0200 From: "Michael S. Tsirkin" To: Jason Wang Cc: virtualization@lists.osdl.org, netdev@vger.kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 3/3] vhost-net: use lock_sock_fast() in peek_head_len() Message-ID: <20110313150646.GA30494@redhat.com> References: <20110117081058.18900.67456.stgit@dhcp-91-7.nay.redhat.com.englab.nay.redhat.com> <20110117081117.18900.48672.stgit@dhcp-91-7.nay.redhat.com.englab.nay.redhat.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20110117081117.18900.48672.stgit@dhcp-91-7.nay.redhat.com.englab.nay.redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-Scanned-By: MIMEDefang 2.68 on 10.5.11.23 Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Mon, Jan 17, 2011 at 04:11:17PM +0800, Jason Wang wrote: > We can use lock_sock_fast() instead of lock_sock() in order to get > speedup in peek_head_len(). > > Signed-off-by: Jason Wang > --- > drivers/vhost/net.c | 4 ++-- > 1 files changed, 2 insertions(+), 2 deletions(-) > > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c > index c32a2e4..50b622a 100644 > --- a/drivers/vhost/net.c > +++ b/drivers/vhost/net.c > @@ -211,12 +211,12 @@ static int peek_head_len(struct sock *sk) > { > struct sk_buff *head; > int len = 0; > + bool slow = lock_sock_fast(sk); > > - lock_sock(sk); > head = skb_peek(&sk->sk_receive_queue); > if (head) > len = head->len; > - release_sock(sk); > + unlock_sock_fast(sk, slow); > return len; > } > Wanted to apply this, but looking at the code I think the lock_sock here is wrong. What we really need is to handle the case where the skb is pulled from the receive queue after skb_peek. However this is not the right lock to use for that, sk_receive_queue.lock is. So I expect the following is the right way to handle this. Comments? Signed-off-by: Michael S. Tsirkin --- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c index 0329c41..5720301 100644 --- a/drivers/vhost/net.c +++ b/drivers/vhost/net.c @@ -213,12 +213,13 @@ static int peek_head_len(struct sock *sk) { struct sk_buff *head; int len = 0; + unsigned long flags; - lock_sock(sk); + spin_lock_irqsave(&sk->sk_receive_queue.lock, flags); head = skb_peek(&sk->sk_receive_queue); - if (head) + if (likely(head)) len = head->len; - release_sock(sk); + spin_unlock_irqrestore(&sk->sk_receive_queue.lock, flags); return len; }