linux-kernel - Re: [PATCH tip/core/rcu 0/4] Programmatic nestable expedited grace periods

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Message-ID: <54E8A986.4090302@linux.intel.com>
Date:	Sat, 21 Feb 2015 07:51:34 -0800
From:	Arjan van de Ven <arjan@...ux.intel.com>
To:	paulmck@...ux.vnet.ibm.com
CC:	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, mingo@...nel.org,
	laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	josh@...htriplett.org, tglx@...utronix.de, rostedt@...dmis.org,
	dhowells@...hat.com, edumazet@...gle.com, dvhart@...ux.intel.com,
	fweisbec@...il.com, oleg@...hat.com, bobby.prani@...il.com
Subject: Re: [PATCH tip/core/rcu 0/4] Programmatic nestable expedited grace
 periods

>>
>> there's a few others as well that I'm chasing down...
>> .. but the flip side, prior to running ring 3 code, why NOT do fast expedites?
>
> It would be good to have before-and-after measurements of actual
> boot time.  Are these numbers available?


To show the boot time, I'm using the timestamp of the "Write protecting" line,
that's pretty much the last thing we print prior to ring 3 execution.

A kernel with default RCU behavior (inside KVM, only virtual devices) looks like this:

[    0.038724] Write protecting the kernel read-only data: 10240k

a kernel with expedited RCU (using the command line option, so that I don't have
to recompile between measurements and thus am completely oranges-to-oranges)

[    0.031768] Write protecting the kernel read-only data: 10240k

which, in percentage, is an 18% improvement.

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