From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Eric Lemoine" Subject: Re: [sungem] proposal for a new locking strategy Date: Sun, 5 Nov 2006 18:52:45 +0100 Message-ID: <5cac192f0611050952w443e6042r11c6c66b0e84685d@mail.gmail.com> References: <5cac192f0611050500m19f72209vc349f235680023a1@mail.gmail.com> <1162731940.28571.245.camel@localhost.localdomain> <5cac192f0611050517q297f5b04w7931788f6dfef3fc@mail.gmail.com> <20061105090254.66710154@localhost.localdomain> <5cac192f0611050928w50127396l2a88978bf97b2bff@mail.gmail.com> <20061105094136.75677aa4@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: "Benjamin Herrenschmidt" , "David S. Miller" , netdev@vger.kernel.org Return-path: Received: from nf-out-0910.google.com ([64.233.182.184]:47909 "EHLO nf-out-0910.google.com") by vger.kernel.org with ESMTP id S1161445AbWKERws (ORCPT ); Sun, 5 Nov 2006 12:52:48 -0500 Received: by nf-out-0910.google.com with SMTP id c2so442318nfe for ; Sun, 05 Nov 2006 09:52:47 -0800 (PST) To: "Stephen Hemminger" In-Reply-To: <20061105094136.75677aa4@localhost.localdomain> Content-Disposition: inline Sender: netdev-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On 11/5/06, Stephen Hemminger wrote: > On Sun, 5 Nov 2006 18:28:33 +0100 > "Eric Lemoine" wrote: > > > > You could also just use net_tx_lock() now. > > > > You mean netif_tx_lock()? > > > > Thanks for letting me know about that function. Yes, I may need it. > > tg3 and bnx2 use it to wake up the transmit queue: > > > > if (unlikely(netif_queue_stopped(tp->dev) && > > (tg3_tx_avail(tp) > TG3_TX_WAKEUP_THRESH))) { > > netif_tx_lock(tp->dev); > > if (netif_queue_stopped(tp->dev) && > > (tg3_tx_avail(tp) > TG3_TX_WAKEUP_THRESH)) > > netif_wake_queue(tp->dev); > > netif_tx_unlock(tp->dev); > > } > > > > 2.6.17 didn't use it. Was it a bug? > > > > Thanks, > > No, it was introduced in 2.6.18. The functions are just a wrapper > around the network device transmit lock that is normally held. > > If the device does not need to acquire the lock during IRQ, it > is a good alternative and avoids a second lock. > > For transmit locking there are three common alternatives: > > Method A: dev->queue_xmit_lock and per-device tx_lock > send: dev->xmit_lock held by caller > dev->hard_start_xmit acquires netdev_priv(dev)->tx_lock > > irq: netdev_priv(dev)->tx_lock acquired > > Method B: dev->queue_xmit_lock only > send: dev->xmit_lock held by caller > irq: schedules softirq (NAPI) > napi_poll: calls netif_tx_lock() which acquires dev->xmit_lock > > Method C: LLTX > set dev->features LLTX > send: no locks held by caller > dev->hard_start_xmit acquires netdev_priv(dev)->tx_lock > irq: netdev_priv(dev)->tx_lock acquired > > Method A is the only one that works with 2.4 and early (2.6.8?) kernels. > Current sungem does Method C, and uses two locks: lock and tx_lock. What I was planning to do is Method B (which current tg3 uses). It seems to me that Method B is better than Method C. What do you think? -- Eric