netdev - Re: [PATCH] Limit size of route cache hash table

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Message-Id: <20090427.054024.94955211.davem@davemloft.net>
Date:	Mon, 27 Apr 2009 05:40:24 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	anton@...ba.org
Cc:	dada1@...mosbay.com, netdev@...r.kernel.org
Subject: Re: [PATCH] Limit size of route cache hash table

From: Anton Blanchard <anton@...ba.org>
Date: Mon, 27 Apr 2009 21:50:07 +1000

> Right now we have no upper limit on the size of the route cache hash table.
> On a 128GB POWER6 box it ends up as 32MB:
> 
>     IP route cache hash table entries: 4194304 (order: 9, 33554432 bytes)
> 
> It would be nice to cap this for memory consumption reasons, but a massive
> hashtable also causes a significant spike when measuring OS jitter.
> 
> With a 32MB hashtable and 4 million entries, rt_worker_func is taking
> 5 ms to complete. On another system with more memory it's taking 14 ms.
> Even though rt_worker_func does call cond_sched() to limit its impact,
> in an HPC environment we want to keep all sources of OS jitter to a minimum.
> 
> With the patch applied we limit the number of entries to 512k which
> can still be overriden by using the rt_entries boot option:
> 
>     IP route cache hash table entries: 524288 (order: 6, 4194304 bytes)
> 
> With this patch rt_worker_func now takes 0.460 ms on the same system.
> 
> Signed-off-by: Anton Blanchard <anton@...ba.org>
> Acked-by: Eric Dumazet <dada1@...mosbay.com>

Applied, thanks!
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