netdev - Re: [PATCH][v2] xfrm: replace NR_CPU with nr_cpu

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Message-ID: <20180620095550.upgvixkjy24a4jo7@breakpoint.cc>
Date:   Wed, 20 Jun 2018 11:55:50 +0200
From:   Florian Westphal <fw@...len.de>
To:     Steffen Klassert <steffen.klassert@...unet.com>
Cc:     Florian Westphal <fw@...len.de>,
        Li RongQing <lirongqing@...du.com>, netdev@...r.kernel.org
Subject: Re: [PATCH][v2] xfrm: replace NR_CPU with nr_cpu_ids

Steffen Klassert <steffen.klassert@...unet.com> wrote:
> On Tue, Jun 19, 2018 at 09:53:49AM +0200, Florian Westphal wrote:
> > Li RongQing <lirongqing@...du.com> wrote:
> > > The default NR_CPUS can be very large, but actual possible nr_cpu_ids
> > > usually is very small. For some x86 distribution, the NR_CPUS is 8192
> > > and nr_cpu_ids is 4, so replace NR_CPU to save some memory
> > 
> > Steffen,
> > 
> > I will soon submit a patch to remove the percpu cache; removal
> > improved performance for at least one user (and by quite a sizeable
> > amount).
> > 
> > Would you consider such removal for ipsec or ipsec-next?
> 
> I think this removel would better fit to ipsec-next.

Agree, it slows things down further for me in my tests.
Problem is that I get quite good re-use of pcpu cache due to
unidirectional flows and only one tunnel.

I suspect that even with tunnel the removal is a win in practice
though, netperf is quite artifical, so I rather trust Kristians results
(real world) than my own.

> considered to apply it to ipsec-next. If you plan
> to remove it, I'll wait for that.

I'll submit once net-next opens.