netdev - Re: [PATCH net-next] mlx4: exploit skb->xmit_more to conditionally send doorbell

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Message-ID: <1411661114.16953.33.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Thu, 25 Sep 2014 09:05:14 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>, Amir Vadai <amirv@...lanox.com>
Subject: Re: [PATCH net-next] mlx4: exploit skb->xmit_more to conditionally
 send doorbell

On Thu, 2014-09-25 at 08:53 -0700, Alexei Starovoitov wrote:
> On Thu, Sep 25, 2014 at 7:17 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> > From: Eric Dumazet <edumazet@...gle.com>
> >
> > skb->xmit_more tells us if another skb is coming next.
> >
> > We need to send doorbell when : xmit_more is not set,
> > or txqueue is stopped (preventing next skb to come immediately)
> >
> > Tested with a modified pktgen version, I got a 40% increase of
> > throughput.
> 
> this is awesome!
> 
> I've been hacking pktgen as well based on Jesper's earlier patch,
> but in slightly different way. Sounds like you already have working
> pktgen with xmit_more. Do you mind sharing it? even rough patch
> would be great.

The plan was to add a 'pburst x' parameter.

Because not only we want to avoid sending the doorbell, but we could
also not doing the spinlock for every start_xmit().

We also can enforce a global [p]rate (say 100000 packets per second),
but still allow pktgen to send burts of x packets to use (and test) this
xmit_more

Nothing ready yet ;)




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