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

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Message-ID: <1370445606.24311.265.camel@edumazet-glaptop>
Date:	Wed, 05 Jun 2013 08:20:06 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Eliezer Tamir <eliezer.tamir@...ux.intel.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 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.

See my following mail about sk_poll_ll()

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