On 12/14/2016 01:57 PM, Pavel Machek wrote:
> Hi!
>
>> So if there is a long time before handling interrupts,
>> I guess that it makes sense that one stream could
>> get an advantage in the net scheduler.
>>
>> If I find the time, and if no one beats me to it, I will try to replace
>> the normal timers with HR timers + a smaller default timeout.
>>
> Can you try something like this? Highres timers will be needed, too,
> but this fixes the logic problem.
>
> You'll need to apply it twice as code is copy&pasted.
>
> Best regards,
Hello Pavel
If I first apply your other fix "stmmac: fix memory barriers",
then I can apply this fix without getting a netdev watchdog timeout on tx
queue0,
and everything appears to work as it should.
Regarding to fairness, I can't really see a difference, with or without your
patch.
I've noticed that for TX, the streams actually stabilize after 5 seconds or so,
but with the default test length of 10 seconds, it's easy to get confused
by the test result summary. So I guess from a fairness point of view,
TX is not really a problem.
For RX fairness, it is very much a real issue. The streams never stabilize.
One key difference is that RX coalescing is implemented by using the
RX watchdog.
Here is an iperf3 run that went for 30 seconds:
[ 4] 0.00-30.00 sec 1.54 GBytes 440 Mbits/sec 0 sender
[ 4] 0.00-30.00 sec 1.54 GBytes 440 Mbits/sec receiver
[ 6] 0.00-30.00 sec 600 MBytes 168 Mbits/sec 0 sender
[ 6] 0.00-30.00 sec 599 MBytes 168 Mbits/sec receiver
[ 8] 0.00-30.00 sec 1.17 GBytes 334 Mbits/sec 0 sender
[ 8] 0.00-30.00 sec 1.17 GBytes 334 Mbits/sec receiver
[SUM] 0.00-30.00 sec 3.29 GBytes 942 Mbits/sec 0 sender
[SUM] 0.00-30.00 sec 3.29 GBytes 942 Mbits/sec receiver
> Pavel
>
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
>
> */
> priv->tx_count_frames += nfrags + 1;
> if (likely(priv->tx_coal_frames > priv->tx_count_frames)) {
> - mod_timer(&priv->txtimer,
> - STMMAC_COAL_TIMER(priv->tx_coal_timer));
> + if (priv->tx_count_frames == nfrags + 1)
> + mod_timer(&priv->txtimer,
> + STMMAC_COAL_TIMER(priv->tx_coal_timer));
> } else {
> priv->tx_count_frames = 0;
> priv->hw->desc->set_tx_ic(desc);
>
>
