netdev - Re: [RFC] GRO scalability

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Message-ID: <20121006051407.GA27390@gondor.apana.org.au>
Date:	Sat, 6 Oct 2012 13:14:07 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>, Jesse Gross <jesse@...ira.com>
Subject: Re: [RFC] GRO scalability

On Sat, Oct 06, 2012 at 07:08:46AM +0200, Eric Dumazet wrote:
> Le samedi 06 octobre 2012 à 12:11 +0800, Herbert Xu a écrit :
> > On Fri, Oct 05, 2012 at 04:52:27PM +0200, Eric Dumazet wrote:
> > > Current GRO cell is somewhat limited :
> > > 
> > > - It uses a single list (napi->gro_list) of pending skbs
> > > 
> > > - This list has a limit of 8 skbs (MAX_GRO_SKBS)
> > > 
> > > - Workloads with lot of concurrent flows have small GRO hit rate but
> > >   pay high overhead (in inet_gro_receive())
> > > 
> > > - Increasing MAX_GRO_SKBS is not an option, because GRO
> > >   overhead becomes too high.
> > 
> > Yeah these were all meant to be addressed at some point.
> > 
> > > - Packets can stay a long time held in GRO cell (there is
> > >   no flush if napi never completes on a stressed cpu)
> > 
> > This should never happen though.  NAPI runs must always be
> > punctuated just to guarantee one card never hogs a CPU.  Which
> > driver causes these behaviour?
> 
> I believe its a generic issue, not specific to a driver.
> 
> napi_gro_flush() is only called from napi_complete() 
> 
> Some drivers (marvell/skge.c & realtek/8139cp.c) calls it only because
> they 'inline' napi_complete()

So which driver has the potential of never doing napi_gro_flush?

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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