Shirley Ma [off-list ref] wrote:

quoted

I have tried this before. There are a couple of issues:

1. the free count will not reduce until you run free_old_xmit_skbs,
   which will not run anymore since the tx queue is stopped.
2. You cannot call free_old_xmit_skbs directly as it races with a
   queue that was just awakened (current cb was due to the delay
   in disabling cb's).

You have to call free_old_xmit_skbs() under netif_queue_stopped()
check to avoid the race.

Yes, that' what I did, when the netif queue stop, don't enable the
queue, just free_old_xmit_skbs(), if not enough freed, then enabling
callback until half of the ring size are freed, then wake the netif
queue. But somehow I didn't reach the performance compared to drop
packets, need to think about it more. :)

Did you check if the number of vmexits increased with this
patch? This is possible if the device was keeping up (and
not going into a stop, start, xmit 1 packet, stop, start
loop). Also maybe you should try for 1/4th instead of 1/2?

MST's delayed signalling should avoid this issue, I haven't
tried both together.

Thanks,

- KK