netdev - RE: [PATCH v9 net-next 5/7] net: simple poll/select low latency socket poll

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Message-ID: <AE90C24D6B3A694183C094C60CF0A2F6026B7270@saturn3.aculab.com>
Date:	Wed, 5 Jun 2013 14:49:31 +0100
From:	"David Laight" <David.Laight@...LAB.COM>
To:	"Eric Dumazet" <eric.dumazet@...il.com>,
	"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

> 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.

Anything calling poll() on 1000 fds probably has performance
issues already! Which is why kevent schemes have been added.

At least the Linux code doesn't use a linked list for
the fd -> 'struct file' map which made poll() O(n^2),
and getting to that number of open fds O(n^3) on
some versions of SVR4.

	David