netdev - Re: [PATCH v2 net-next] bridge: Add ability to enable TSO

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Date:	Fri, 9 Jan 2015 14:10:13 -0500 (EST)
From:	Pankaj Gupta <pagupta@...hat.com>
To:	Toshiaki Makita <makita.toshiaki@....ntt.co.jp>
Cc:	"David S . Miller" <davem@...emloft.net>,
	Stephen Hemminger <stephen@...workplumber.org>,
	netdev@...r.kernel.org, bridge@...ts.linux-foundation.org
Subject: Re: [PATCH v2 net-next] bridge: Add ability to enable TSO


> > 
> >>
> >> Currently a bridge device turns off TSO feature if no bridge ports
> >> support it. We can always enable it, since packets can be segmented on
> >> ports by software as well as on the bridge device.
> >> This will reduce the number of packets processed in the bridge.
> >>
> >> Signed-off-by: Toshiaki Makita <makita.toshiaki@....ntt.co.jp>
> >> ---
> >> v2: Use an existing helper function.
> >>
> >>  net/bridge/br_if.c | 1 +
> >>  1 file changed, 1 insertion(+)
> >>
> >> diff --git a/net/bridge/br_if.c b/net/bridge/br_if.c
> >> index ed307db..81e49fb 100644
> >> --- a/net/bridge/br_if.c
> >> +++ b/net/bridge/br_if.c
> >> @@ -424,6 +424,7 @@ netdev_features_t br_features_recompute(struct
> >> net_bridge
> >> *br,
> >>  		features = netdev_increment_features(features,
> >>  						     p->dev->features, mask);
> >>  	}
> >> +	features = netdev_add_tso_features(features, mask);
> > 
> > Just a doubt. Are we inducing latency if source has traffic at very low
> > rate.
> > I mean by default do we need it?
> 
> Is your concern tcp_tso_should_defer() in tcp_write_xmit()?
yes.

> If so, since TSO packet is created by GSO even without this patch, this
> should not increase latency there.
> This patch just delays the point of software segmentation from the
> bridge device to its port.

I think now I got your point. 

Thanks,
Pankaj
> 
> Thanks,
> Toshiaki Makita
> 
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