linux-kernel - Re: [patch 00/13] Syslets, "Threadlets", generic AIO support, v3

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Date:	Tue, 27 Feb 2007 20:06:10 +0300
From:	Evgeniy Polyakov <johnpol@....mipt.ru>
To:	Eric Dumazet <dada1@...mosbay.com>
Cc:	Davide Libenzi <davidel@...ilserver.org>,
	Ingo Molnar <mingo@...e.hu>,
	Ulrich Drepper <drepper@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Christoph Hellwig <hch@...radead.org>,
	Andrew Morton <akpm@....com.au>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Zach Brown <zach.brown@...cle.com>,
	"David S. Miller" <davem@...emloft.net>,
	Suparna Bhattacharya <suparna@...ibm.com>,
	Jens Axboe <jens.axboe@...cle.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [patch 00/13] Syslets, "Threadlets", generic AIO support, v3

On Tue, Feb 27, 2007 at 05:58:14PM +0100, Eric Dumazet (dada1@...mosbay.com) wrote:
> I believe one advantage of epoll is it uses standard mechanism (mandated for 
> poll()/select() ), while kevent adds some glue and kevent_storage in some 
> structures (struct inode, struct file, ...), thus adding some extra code and 
> extra storage in hot paths. Yes there might be a gain IF most users of these 
> path want kevent. But other users pay the price (larger kernel code and 
> data), that you cannot easily bench.
> 
> Using or not epoll has nearly zero cost over standard kernel (only struct file 
> has some extra storage)

Well, that's a price - any event which wants to be supported needs to
store for events - kevent_storage is a list_head plus spinlock and
pointer to itself (with all current users that pointer can be removed and
access transferred to container_of()) - it is exactly as in epoll storage - 
both were created with the smallest possible overhead in mind.

-- 
	Evgeniy Polyakov
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