On Tue, Sep 02, 2014 at 09:15:18AM +0300, Eliezer Tamir wrote:

On 02/09/2014 06:29, Jason Wang wrote:

quoted

On 09/01/2014 02:39 PM, Eliezer Tamir wrote:

quoted

On 29/08/2014 06:08, Jason Wang wrote:

quoted

quoted

Yes, but rx busy polling only works in process context and does not
disable bh, so it may be not an issue.

sk_busy_loop() uses rcu_read_lock_bh(), so it does run with bh disabled.

True, so we need probably also exit the loop when there are pending bhs.

I'm not so sure, in the typical busy poll scenario, the incoming
traffic is the most time-critical thing in the system.
It's so important that you are willing to trade lots of CPU power
for better latency. The user has decided that he wants to dedicate
this CPU mostly for that. This is not something that plays nice with
other apps, but this is what the user wants.

I think most applications wouldn't interpret this flag as "burn up CPU I don't
care what is the result", what apps want is more of "maximise throughput
and minimise latency even if throughput/CPU ratio goes down".
Jason posted benchmarks that show throughput going up because other
processes get more of a chance to run, so this seems consistent
with that goal.

So, you definitely don't want to starve any bh, and you should
regularly re-enable bh's, but you also don't want to stop everything
at any time a bh is scheduled.

You also want network processing on the queues that are busy polled
to come through busy polling and not through NAPI, which is run in bh
context.

-Eliezer