On 11/5/06, Stephen Hemminger <[EMAIL PROTECTED]> wrote:
On Sun, 5 Nov 2006 18:52:45 +0100 "Eric Lemoine" <[EMAIL PROTECTED]> wrote:> On 11/5/06, Stephen Hemminger <[EMAIL PROTECTED]> wrote: > > On Sun, 5 Nov 2006 18:28:33 +0100 > > "Eric Lemoine" <[EMAIL PROTECTED]> 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? B is better than C because the transmit logic doesn't have to spin in the case of lock contention, but it is not a big difference.
Current sungem does C but uses try_lock() to acquire its private tx_lock. So it doesn't spin either in case of contention.
You can only use B if you do Tx completion outside of hard IRQ.
Because qdisk_restart() is called with bh disabled *but* with irq enabled, right? -- Eric - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
