From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eric Dumazet <eric.dumazet@gmail.com>
Subject: Re: [PATCH] net: gro: selective flush of packets
Date: Sun, 07 Oct 2012 07:29:47 +0200
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Cc: David Miller <davem@davemloft.net>,
	netdev <netdev@vger.kernel.org>, Jesse Gross <jesse@nicira.com>,
	Tom Herbert <therbert@google.com>,
	Yuchung Cheng <ycheng@google.com>
To: Herbert Xu <herbert@gondor.apana.org.au>
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	On Sun, 2012-10-07 at 08:32 +0800, Herbert Xu wrote:
> On Sat, Oct 06, 2012 at 08:08:49PM +0200, Eric Dumazet wrote:
> >
> > @@ -3981,8 +3996,17 @@ static void net_rx_action(struct softirq_action *h)
> >  				local_irq_enable();
> >  				napi_complete(n);
> >  				local_irq_disable();
> > -			} else
> > +			} else {
> > +				if (n->gro_list) {
> > +					/* flush too old packets
> > +					 * If HZ < 1000, flush all packets.
> > +					 */
> > +					local_irq_enable();
> > +					napi_gro_flush(n, HZ >= 1000);
> > +					local_irq_disable();
> > +				}
> >  				list_move_tail(&n->poll_list, &sd->poll_list);
> > +			}
> 
> Why don't we just always flush everything?

This is what I tried first, but it lowered performance on several
typical workloads.

Using this simple heuristic increases performance.