netdev - Re: [PATCH net-next] net: percpu net

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Message-ID: <20101007103051.63b5177c@nehalam>
Date:	Thu, 7 Oct 2010 10:30:51 -0700
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Miller <davem@...emloft.net>, netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next] net: percpu net_device refcount

On Thu, 07 Oct 2010 19:12:35 +0200
Eric Dumazet <eric.dumazet@...il.com> wrote:

> We tried very hard to remove all possible dev_hold()/dev_put() pairs in
> network stack, using RCU conversions.
> 
> There is still an unavoidable device refcount change for every dst we
> create/destroy, and this can slow down some workloads (routers or some
> app servers)
> 
> We can switch to a percpu refcount implementation, now dynamic per_cpu
> infrastructure is mature. On a 64 cpus machine, this consumes 256 bytes
> per device.
> 

It makes sense, but what about 256 cores and 1024 Vlans?
That adds up to 4M of memory which is might be noticeable.


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