netdev - Re: [PATCH] poll: Avoid extra wakeups in select/poll

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Message-ID: <49F77108.7060509@cosmosbay.com>
Date:	Tue, 28 Apr 2009 23:11:36 +0200
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Eric Dumazet <dada1@...mosbay.com>
CC:	Christoph Lameter <cl@...ux.com>,
	linux kernel <linux-kernel@...r.kernel.org>,
	Andi Kleen <andi@...stfloor.org>,
	David Miller <davem@...emloft.net>, jesse.brandeburg@...el.com,
	netdev@...r.kernel.org, haoki@...hat.com, mchan@...adcom.com,
	davidel@...ilserver.org, Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] poll: Avoid extra wakeups in select/poll

Eric Dumazet a écrit :
> Christoph Lameter a écrit :
>> On Tue, 28 Apr 2009, Eric Dumazet wrote:
>>
>>> The one that did improved your udpping 'bench' :)
>>>
>>> http://git2.kernel.org/?p=linux/kernel/git/davem/net-2.6.git;a=commitdiff;h=bf368e4e70cd4e0f880923c44e95a4273d725ab4
>> Well yes that is git2p1. The measurements that we took showed not much of
>> an effect as you see.
>>
> 
> It depends of coalescing parameters of NIC.
> 
> BNX2 interrupts first handle TX completions, then RX events.
> So If by the
> 

Sorry for the previous message...

If by the time interrupt comes to the host, TX was handled right before RX event,
the extra wakeup is not a problem, because incoming frame will be delivered into
socket queue right before awaken thread tries to pull it.

On real workloads (many incoming/outgoing frames), then avoiding extra wakeups is
a win, regardless of coalescing parameters and cpu affinities...

On uddpping, I had prior to the patch about 49000 wakeups per second,
and after patch about 26000 wakeups per second (matches number of incoming
udp messages per second)

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