netdev - Re: [PATCH 2/2] lib: cpu_rmap: CPU affinity reverse-mapping

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Date:	Tue, 04 Jan 2011 23:19:02 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Ben Hutchings <bhutchings@...arflare.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	David Miller <davem@...emloft.net>,
	Tom Herbert <therbert@...gle.com>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	linux-net-drivers@...arflare.com
Subject: Re: [PATCH 2/2] lib: cpu_rmap: CPU affinity reverse-mapping

Le mardi 04 janvier 2011 à 22:04 +0000, Ben Hutchings a écrit :

> get_rps_cpu() will need to read from an arbitrary entry in cpu_rmap (not
> the current CPU's entry) for each new flow and for each flow that went
> idle for a while.  That's not fast path but it is part of the data path,
> not the control path.
> 

Hmm, I call this fast path :(

> > Cache lines dont matter. I was not concerned about speed but memory
> > needs.
> > 
> > NR_CPUS can be 4096 on some distros, that means a 32Kbyte allocation.
> > 
> > Really, you'll have to have very strong arguments to introduce an
> > [NR_CPUS] array in the kernel today.
> 
> I could replace this with a pointer to an array of size
> num_possible_cpus().  But I think per_cpu is wrong here.

Yes, an dynamic array is acceptable

You probably mean nr_cpu_ids 




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