netdev - Re: [PATCH v6] net: batch skb dequeueing from softnet input_pkt

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Message-ID: <20100503032227.268613ac@infradead.org>
Date:	Mon, 3 May 2010 03:22:27 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	David Miller <davem@...emloft.net>, hadi@...erus.ca,
	xiaosuo@...il.com, therbert@...gle.com, shemminger@...tta.com,
	netdev@...r.kernel.org, lenb@...nel.org
Subject: Re: [PATCH v6] net: batch skb dequeueing from softnet
 input_pkt_queue

On Mon, 03 May 2010 07:17:14 +0200
Eric Dumazet <eric.dumazet@...il.com> wrote:

> Le dimanche 02 mai 2010 à 20:50 -0700, Arjan van de Ven a écrit :
> 
> > we effectively do that. The thing is that C2 is so low cost normally
> > that it's still worth it even at 20k wakeups...
> > 
> > this is where the bios tells us how "heavy" the states are....
> > and 64 usec... is just not very much.
> 
> Maybe its low cost, (apparently, it is, since I can reach ~900.000
> ipis on my 16 cores machine) but multiply this by 16 or 32 or 64
> cpus, and clockevents_notify() cost appears to be a killer, all cpus
> compete on a single lock.
> 
> Maybe this notifier could use RCU ?

could this be an artifact of the local apic stopping in deeper C states?
(which is finally fixed in the Westmere generation)



-- 
Arjan van de Ven 	Intel Open Source Technology Centre
For development, discussion and tips for power savings, 
visit http://www.lesswatts.org
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