netdev - Re: [RFC PATCH] net: Require socket to allow XPS to set queue mapping

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Message-ID: <1472159297.14381.162.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Thu, 25 Aug 2016 14:08:17 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Rick Jones <rick.jones2@....com>
Cc:     Alexander Duyck <alexander.h.duyck@...el.com>,
        netdev@...r.kernel.org
Subject: Re: [RFC PATCH] net: Require socket to allow XPS to set queue
 mapping

On Thu, 2016-08-25 at 13:32 -0700, Rick Jones wrote:
> On 08/25/2016 12:49 PM, Eric Dumazet wrote:
> > On Thu, 2016-08-25 at 12:23 -0700, Alexander Duyck wrote:
> >> A simpler approach is provided with this patch.  With it we disable XPS any
> >> time a socket is not present for a given flow.  By doing this we can avoid
> >> using XPS for any routing or bridging situations in which XPS is likely
> >> more of a hinderance than a help.
> >
> > Yes, but this will destroy isolation for people properly doing VM cpu
> > pining.
> 
> Why not simply stop enabling XPS by default. Treat it like RPS and RFS 
> (unless I've missed a patch...). The people who are already doing the 
> extra steps to pin VMs can enable XPS in that case.  It isn't clear that 
> one should always pin VMs - for example if a (public) cloud needed to 
> oversubscribe the cores.
> 

When XPS was submitted, it was _not_ enabled by default and 'magic'

Some NIC vendors decided it was a good thing, you should complain to
them ;)