netdev - Re: [PATCH v2] ipv4: percpu nh_rth

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Message-Id: <20120731.144311.1857420608722189065.davem@davemloft.net>
Date:	Tue, 31 Jul 2012 14:43:11 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	netdev@...r.kernel.org, alexander.h.duyck@...el.com
Subject: Re: [PATCH v2] ipv4: percpu nh_rth_output cache

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Tue, 31 Jul 2012 17:45:30 +0200

> From: Eric Dumazet <edumazet@...gle.com>
> 
> Input path is mostly run under RCU and doesnt touch dst refcnt
> 
> But output path on forwarding or UDP workloads hits
> badly dst refcount, and we have lot of false sharing, for example
> in ipv4_mtu() when reading rt->rt_pmtu
> 
> Using a percpu cache for nh_rth_output gives a nice performance
> increase at a small cost.
> 
> 24 udpflood test on my 24 cpu machine (dummy0 output device)
> (each process sends 1.000.000 udp frames, 24 processes are started)
> 
> before : 5.24 s
> after : 2.06 s
> For reference, time on linux-3.5 : 6.60 s
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Applied.

However I think fib_create_info() should fail if it cannot alloc_percpu()
successfully, instead of having funny logic in rt_cache_route().
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