On Mon, 2007-02-07 at 17:21 -0700, Michael Chan wrote:
[Matt, please include the count in the fix per previous email]
> Only base_flags and mss are needed and these can be determined right
> before sending the frame. So is it better not to store these in the
> skb->cb at all?
long answer:
My goal with storing these values and computing them was to do certain
things that dont require holding the netif_tx_lock within a batch as
well. Evaluating the packet metadata and formating the packet to be
ready for stashing into DMA was one thing i could do outside of holding
the lock easily - and running that in loop of 100 packets amortizes the
instruction cache and allows me (when i get to it) to hold the lock for
a lot less computation.
In the e1000 for example i was able to go as far as computing how many
descriptors are needed per skb and stashing those in the skb->cb; the
way the tg3 is structured makes doing all that needing some big changes.
So to answer your question: It would be nice if i could keep the skb->cb
for now and we can get rid of it later if deemed a nuisance for
batching.
>
> + dcount = tg3_tx_avail(tp);
> if (unlikely(netif_queue_stopped(tp->dev) &&
> - (tg3_tx_avail(tp) > TG3_TX_WAKEUP_THRESH(tp)))) {
> + (dcount > TG3_TX_WAKEUP_THRESH(tp)))) {
> netif_tx_lock(tp->dev);
> + tp->dev->xmit_win = 1;
> if (netif_queue_stopped(tp->dev) &&
> - (tg3_tx_avail(tp) > TG3_TX_WAKEUP_THRESH(tp)))
> + (dcount > TG3_TX_WAKEUP_THRESH(tp))) {
> netif_wake_queue(tp->dev);
> + tp->dev->xmit_win = dcount;
> + }
> netif_tx_unlock(tp->dev);
> }
> }
>
> This is also not right. tg3_tx() runs without netif_tx_lock().
> tg3_tx_avail() can change after you get the netif_tx_lock() and we must
> get the updated value again. If we just rely on dcount, we can call
> wake_queue() when the ring is full, or there may be no wakeup when the
> ring is empty.
You are right, I was trying to be a smart-ass there so i didnt have to
fold the lines (for readability). Can you or Matt restore it to the way
it was originally while keeping the xmit_win update and just send me a
patch?
Thanks a lot Michael and Matt for looking at this and improving it.
Maybe i should switch all my nics to tg3 from now on ;->
cheers,
jamal
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