netdev - Re: [RFC] GRO scalability

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Date:	Sat, 06 Oct 2012 07:08:46 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>, Jesse Gross <jesse@...ira.com>
Subject: Re: [RFC] GRO scalability

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()



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