On Thu, 2006-03-08 at 11:05 -0700, Michael Chan wrote: > On Thu, 2006-08-03 at 09:36 -0700, Brandeburg, Jesse wrote: > > > I followed the example of tg3 when attempting to optimize this code. For > > the normal case we remove a lock acquisition. Jamals case is not normal. > > :-) > > > > we specifically added this lock originally to fix a problem we saw where > > the netif_stop and netif_start would race, and we would end up with a > > queue that was stopped, and no way to restart it because we didn't have > > any more TX packets to clean up (even if we DID get an interrupt from a > > receive) > > > Yep, I agree that the lock is necessary. The reason is that > hard_start_xmit and xmit_completion can be running concurrently and they > can miss each other and cause the tx ring to be stopped forever. >
Logic is you are stopped, the tx path can _never_ be entered by the core. If it is you have a bug somewhere else. Tx and rx do run concurently but not when you are stopped. > In the case of tg3's hard_start_xmit, after stopping the queue, we need > to check if we should wake the queue right away in case xmit_completion > just finished cleaning the tx ring and just missed the queue_stopped > condition. Is this to protect against some hardware bug? > Because the netif_wake_queue can be called in 2 places, you > need the lock. Without the lock, the queue can be waken up at the wrong > time and may cause hard_start_xmit to be called with an empty tx ring. > Yes in your case you need to hold the lock but not in the e1000 case. I dont understand though why you need to check for wake in the tx path. cheers, jamal - 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
