From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jakub Kicinski <jakub.kicinski@netronome.com>
Subject: Re: [RFC] net: bump the default number of RSS queues
Date: Wed, 4 Apr 2018 17:08:45 -0700
Message-ID: <20180404170845.77c54f38@cakuba.netronome.com>
References: <20180404001422.6080-1-jakub.kicinski@netronome.com>
        <3f6f40f3-cca2-0f43-8940-05003da88524@gmail.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Cc: davem@davemloft.net, netdev@vger.kernel.org, brouer@redhat.com,
        alexander.duyck@gmail.com, oss-drivers@netronome.com
To: Eric Dumazet <eric.dumazet@gmail.com>
Return-path: <netdev-owner@vger.kernel.org>
Received: from mail-qt0-f195.google.com ([209.85.216.195]:40473 "EHLO
        mail-qt0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1752529AbeDEAIu (ORCPT
        <rfc822;netdev@vger.kernel.org>); Wed, 4 Apr 2018 20:08:50 -0400
Received: by mail-qt0-f195.google.com with SMTP id g5so25159118qth.7
        for <netdev@vger.kernel.org>; Wed, 04 Apr 2018 17:08:50 -0700 (PDT)
In-Reply-To: <3f6f40f3-cca2-0f43-8940-05003da88524@gmail.com>
Sender: netdev-owner@vger.kernel.org
List-ID: <netdev.vger.kernel.org>

On Tue, 3 Apr 2018 17:20:49 -0700, Eric Dumazet wrote:
> On 04/03/2018 05:14 PM, Jakub Kicinski wrote:
> > Some popular NIC vendors are not adhering to
> > netif_get_num_default_rss_queues() which leads to users being
> > surprised and filing bugs :)  Bump the number of default RX
> > queues to something more reasonable for modern machines.
> > 
> > Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
> > ---
> > I'm mostly wondering what's the policy on this default?  When
> > should it be applied?  Why was 8 chosen as the default?  We
> > can abandon using netif_get_num_default_rss_queues() for the
> > nfp but I wonder what's the correct course of action here...
> > Should new drivers use netif_get_num_default_rss_queues() for
> > example?
> > 
> >  include/linux/netdevice.h | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> > index 2a2d9cf50aa2..26fe145ada2a 100644
> > --- a/include/linux/netdevice.h
> > +++ b/include/linux/netdevice.h
> > @@ -3260,7 +3260,7 @@ static inline unsigned int get_netdev_rx_queue_index(
> >  }
> >  #endif
> >  
> > -#define DEFAULT_MAX_NUM_RSS_QUEUES	(8)
> > +#define DEFAULT_MAX_NUM_RSS_QUEUES	(64)
> >  int netif_get_num_default_rss_queues(void);  
> 
> There is no evidence having so many queues is beneficial.
> 
> Too many queues -> lots of overhead in many cases.
> 
> So I would rather not touch this, unless you can present good numbers ;)

Thank you for the comment!  I don't have convincing number it was more
of a matter of consistency :)  

Now I think I forgot about aRFS, when aRFS support for the nfp is added
we will probably start ignoring the default as well.