netdev - Re: TCPBacklogDrops during aggressive bursts of traffic

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Message-ID: <1337272654.3403.20.camel@edumazet-glaptop>
Date:	Thu, 17 May 2012 18:37:34 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Kieran Mansley <kmansley@...arflare.com>
Cc:	Ben Hutchings <bhutchings@...arflare.com>, netdev@...r.kernel.org
Subject: Re: TCPBacklogDrops during aggressive bursts of traffic

On Thu, 2012-05-17 at 17:31 +0100, Kieran Mansley wrote:
> On Tue, 2012-05-15 at 19:01 +0200, Eric Dumazet wrote:
> > You could try setting tcp_adv_win_scale to -2
> 
> I've been unable to reproduce this at all this afternoon (not sure why)
> so haven't been able to try that suggestion yet.
> 
> From looking in to what it does it sounds like it could well help, but
> only in the sense of tuning the system to make it harder to hit the race
> rather than fixing the race altogether.  Similarly for fixing
> skb->truesize (we spotted this last week when we first hit the problem,
> and adjusting it didn't make much difference).

Hmm, I was not suggesting running production servers with this setting,
only do an experiment.

With net-next and tcp coalescing, I no longer have TCPBacklogDrops /
collapses, but I dont have sfc card/driver.


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