linux-kernel - Re: [RFC PATCH 1/8] Convert the RCU tasklet into a softirq

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Message-ID: <Pine.LNX.4.58.0707161638460.18244@gandalf.stny.rr.com>
Date:	Mon, 16 Jul 2007 16:44:09 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Christoph Hellwig <hch@...radead.org>,
	john stultz <johnstul@...ibm.com>,
	Oleg Nesterov <oleg@...sign.ru>,
	Dipankar Sarma <dipankar@...ibm.com>,
	"David S. Miller" <davem@...emloft.net>, kuznet@....inr.ac.ru,
	Jonathan Corbet <corbet@....net>,
	Arjan van de Ven <arjan@...radead.org>,
	Arnd Bergmann <arnd@...db.de>
Subject: Re: [RFC PATCH 1/8] Convert the RCU tasklet into a softirq

On Mon, 16 Jul 2007, Linus Torvalds wrote:

>
> Btw, are there any numbers on this? Is this whole thing actually
> noticeable?

Besides the obvious removal of code?

The old way actually made an effort to create per_cpu tasklets!  So that
the tasklets *can* run simultaneously, making it in essense a softirq.
Since tasklets are implemented by the softirq, with a lot of code to make
a tasklet function run only on one CPU at a time, and it can run on any
CPU.  By converting the rcu tasklet (which had work to make it act like a
softirq) to just be a softirq, we removed all the extra overhead of a
tasklet.

But to answer your question.  No, I didn't take any actual measurements.
The changes just seemed obvious to me (and others).

-- Steve

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