netdev - Re: Problem with fragmented packets on tun/tap interface

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Message-ID: <1438341695.2748.11.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Fri, 31 Jul 2015 13:21:35 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Prashant Upadhyaya <praupadhyaya@...il.com>
Cc:	netdev <netdev@...r.kernel.org>
Subject: Re: Problem with fragmented packets on tun/tap interface

On Fri, 2015-07-31 at 16:42 +0530, Prashant Upadhyaya wrote:
> On Fri, Jul 31, 2015 at 1:26 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> > On Fri, 2015-07-31 at 12:30 +0530, Prashant Upadhyaya wrote:
> >
> >> The delays work for me but is clearly not good for the performance of
> >> the slow path. And more importantly, I was looking for a fundamental
> >> reason regarding why it works with delays and why not without it. The
> >> issue is reproducible with a big ping (3.11.10-301.fc20.x86_64)
> >
> > How big ping needs to be to reproduce the problem ?
> >
> >
> 
> If the MTU is 1500, I start getting problems anywhere starting from
> 2900 bytes and surely comes when further big pings are used eg. 10 K.
> (ping <IP> -s <Size> eg. ping 10.3.10.244 -s 10000)
> And the big pings do work, as I said, with the delay hack.

It might help trying this while you receive such frags :

perf record -a -g skb:kfree_skb sleep 10

...

perf report



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