linux-kernel - Re: [PATCH v9 net-next 5/7] net: simple poll/select low latency socket poll

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Date:	Wed, 05 Jun 2013 18:47:14 +0300
From:	Eliezer Tamir <eliezer.tamir@...ux.intel.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	David Miller <davem@...emloft.net>, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org,
	Jesse Brandeburg <jesse.brandeburg@...el.com>,
	Don Skidmore <donald.c.skidmore@...el.com>,
	e1000-devel@...ts.sourceforge.net,
	Willem de Bruijn <willemb@...gle.com>,
	Ben Hutchings <bhutchings@...arflare.com>,
	Andi Kleen <andi@...stfloor.org>, HPA <hpa@...or.com>,
	Eilon Greenstien <eilong@...adcom.com>,
	Or Gerlitz <or.gerlitz@...il.com>,
	Amir Vadai <amirv@...lanox.com>,
	Eliezer Tamir <eliezer@...ir.org.il>
Subject: Re: [PATCH v9 net-next 5/7] net: simple poll/select low latency socket
 poll

On 05/06/2013 18:20, Eric Dumazet wrote:
> On Wed, 2013-06-05 at 16:41 +0300, Eliezer Tamir wrote:
>> On 05/06/2013 16:30, Eric Dumazet wrote:
>
>>> I am a bit uneasy with this one, because an applicatio polling() on one
>>> thousand file descriptors using select()/poll(), will call sk_poll_ll()
>>> one thousand times.
>>
>> But we call sk_poll_ll() with nonblock set, so it will only test once
>> for each socket and not loop.
>>
>> I think this is not as bad as it sounds.
>> We still honor the time limit on how long to poll.
>
> We still call ndo_ll_poll() a thousand times, and probably do a
> spinlock/unlock a thousand times in the driver.
>
> I would definitely be convinced if you give us some performance numbers
> of a poll() on a thousand tcp sockets for example.

So with 1000 sockets this is defiantly not a win
sockperf with 1000 udp sockets

sysctl   50         0
select 178.5 us / 130.0 us
poll   188.6 us / 130.0 us

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