On Tue, 2014-08-19 at 11:52 -0700, Benjamin Poirier wrote:
> @@ -7838,11 +7838,14 @@ static int tg3_tso_bug(struct tg3 *tp, struct
> tg3_napi *tnapi,
> struct netdev_queue *txq, struct sk_buff *skb)
> {
> struct sk_buff *segs, *nskb;
> - u32 frag_cnt_est = skb_shinfo(skb)->gso_segs * 3;
>
> - /* Estimate the number of fragments in the worst case */
> - if (unlikely(tg3_tx_avail(tnapi) <= frag_cnt_est)) {
> + if (unlikely(tg3_tx_avail(tnapi) <= skb_shinfo(skb)->gso_segs)) {
> + trace_printk("stopping queue, %d <= %d\n",
> + tg3_tx_avail(tnapi), skb_shinfo(skb)->gso_segs);
> netif_tx_stop_queue(txq);
> + trace_printk("stopped queue\n");
> + tnapi->wakeup_thresh = skb_shinfo(skb)->gso_segs;
> + BUG_ON(tnapi->wakeup_thresh >= tnapi->tx_pending);
>
> /* netif_tx_stop_queue() must be done before checking
> * checking tx index in tg3_tx_avail() below, because in
I don't quite understand this logic and I must be missing something.
gso_segs is the number of TCP segments the large packet will be broken
up into. If it exceeds dev->gso_max_segs, it means it exceeds
hardware's capabilty and it will do GSO instead of TSO. But in this
case in tg3_tso_bug(), we are doing GSO and we may not have enough DMA
descriptors to do GSO. Each gso_seg typically requires 2 DMA
descriptors.
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