netdev - Re: [RFC PATCH net-next 10/10] ipv6: Create percpu rt6

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Message-Id: <1428961585.3872951.253274201.0C14EC83@webmail.messagingengine.com>
Date:	Mon, 13 Apr 2015 23:46:25 +0200
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Martin KaFai Lau <kafai@...com>,
	Steffen Klassert <steffen.klassert@...unet.com>
Cc:	netdev@...r.kernel.org, kernel-team@...com
Subject: Re: [RFC PATCH net-next 10/10] ipv6: Create percpu rt6_info

On Mon, Apr 13, 2015, at 22:16, Martin KaFai Lau wrote:
> On Mon, Apr 13, 2015 at 12:59:44PM +0200, Steffen Klassert wrote:
> > On Fri, Apr 10, 2015 at 06:59:36PM -0700, Martin KaFai Lau wrote:
> > 
> > > diff --git a/include/uapi/linux/ipv6_route.h b/include/uapi/linux/ipv6_route.h
> > > index 2be7bd1..f6598d1 100644
> > > --- a/include/uapi/linux/ipv6_route.h
> > > +++ b/include/uapi/linux/ipv6_route.h
> > > @@ -34,6 +34,7 @@
> > >  #define RTF_PREF(pref)	((pref) << 27)
> > >  #define RTF_PREF_MASK	0x18000000
> > >  
> > > +#define RTF_PCPU	0x40000000
> > 
> > This percpu flag is something internal, should IMO not be added
> > to the uapi.
> Make sense.  Where may be the right place for it?
> 
> It seems 'uapi/linux/ipv6_route.h' is the one which has all IPv6 flags
> laid out.
> It makes modification easier since it tells us which bit is still
> available.

Actually, we expose those flags via /proc/net/ipv6_route. I would be
fine keeping it in uapi.

> How about we add a comment to 'uapi/linux/ipv6_route.h' and move the
> '#define'
> to 'linux/ipv6_route.h'?
> 
> > 
> > > @@ -1978,8 +2100,13 @@ static void ip6_rt_copy_init(struct rt6_info *rt,
> > >  static struct rt6_info *ip6_rt_cache_alloc(struct rt6_info *ort,
> > >  					   const struct in6_addr *dest)
> > >  {
> > > -	struct rt6_info *rt = ip6_dst_alloc(dev_net(ort->dst.dev), ort->dst.dev,
> > > -					    0, ort->rt6i_table);
> > > +	struct rt6_info *rt;
> > > +
> > > +	if (ort->rt6i_flags & RTF_PCPU)
> > > +		ort = (struct rt6_info *)ort->dst.from;
> > > +
> > > +	rt = __ip6_dst_alloc(dev_net(ort->dst.dev), ort->dst.dev,
> > > +			     0, ort->rt6i_table);
> > 
> > Why don't you allocate the percpu resources for cached routes?
> > I think using ip6_dst_alloc() would be better here, cached routes
> > could benefit from this too.
> Not sure if we want to open up percpu cache opportunity for RTF_CACHE
> route after receiving ICMPv6 too-big from remote peers and some of our
> machines
> have a lot of CPU (like 40), so I opt not to do it.
> If we do this, we probably need to modify the gc and its related counting
> also.

I agree that we should handle those exceptions as a kind of "slow" path.

Bye,
Hannes
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