netdev - Re: r8169 regression: UDP packets dropped intermittantly

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Message-ID: <1447970316.22599.257.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Thu, 19 Nov 2015 13:58:36 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Francois Romieu <romieu@...zoreil.com>
Cc:	Jonathan Woithe <jwoithe@...ad.com.au>, netdev@...r.kernel.org
Subject: Re: r8169 regression: UDP packets dropped intermittantly

On Thu, 2015-11-19 at 22:44 +0100, Francois Romieu wrote:
> Eric Dumazet <eric.dumazet@...il.com> :
> [...]
> > This looks like a race when/if RX happens very shortly after one
> > transmit.
> > 
> > Francois, are we really saving lot of cpu cycles testing status ?
> 
> I'm not sure. An extra smp_rmb and three cache lines at most when
> there really isn't any work ? Probably not worth it.
> 
> Can you clarify which kind of race you're thinking about ?

I was mostly thinking of some hardware bug.

Or maybe a software barrier is missing, but I could not see it.

(Assuming rtl_get_events() is accurate, ie really returns a mask of
pending events in all circumstances, including if run in // from
rtl_slow_event_work() and rtl8169_poll())



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