linux-kernel - Re: Dynamic configure max

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Date:	Tue, 28 Jul 2009 16:03:08 +0200
From:	Andreas Mohr <andi@...as.de>
To:	Andreas Mohr <andi@...as.de>
Cc:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
	Corrado Zoccolo <czoccolo@...il.com>,
	LKML <linux-kernel@...r.kernel.org>, linux-acpi@...r.kernel.org
Subject: Re: Dynamic configure max_cstate

On Tue, Jul 28, 2009 at 12:11:35PM +0200, Andreas Mohr wrote:
> As a very quick test, I tried a
> while :; do :; done
> loop in shell and renicing shell to 19 (to keep my CPU out of ACPI idle),
> but bonnie -s 100 results initially looked promising yet turned out to
> be inconsistent. The real way to test this would be idle=poll.
> My test system was Athlon XP with /proc/acpi/processor/CPU0/power
> latencies of 000 and 100 (the maximum allowed value, BTW) for C1/C2.

OK, I just tested it properly.
Rebooted, did 5 bonnie -s 100 with ACPI idle, rebooted and did another 5
bonnie -s 100 with idle=poll, results:


$ cat bonnie_ACPI_* /tmp/line bonnie_poll_*
              -------Sequential Output-------- ---Sequential Input-- --Random--
              -Per Char- --Block--- -Rewrite-- -Per Char- --Block--- --Seeks---
Machine    MB K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU  /sec %CPU
       1* 100 20084 95.3 19037  9.5 12286  4.7 18074 99.6 581752 96.6 28792.3 93.6
              -------Sequential Output-------- ---Sequential Input-- --Random--
              -Per Char- --Block--- -Rewrite-- -Per Char- --Block--- --Seeks---
Machine    MB K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU  /sec %CPU
       1* 100 19235 93.5 24591 11.8 13916  4.3 17934 99.8 604429 100.3 27993.8 98.0
              -------Sequential Output-------- ---Sequential Input-- --Random--
              -Per Char- --Block--- -Rewrite-- -Per Char- --Block--- --Seeks---
Machine    MB K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU  /sec %CPU
       1* 100 17221 86.3 30591 16.1 15404  5.4 18689 99.3 593296 92.7 28146.0 98.5
              -------Sequential Output-------- ---Sequential Input-- --Random--
              -Per Char- --Block--- -Rewrite-- -Per Char- --Block--- --Seeks---
Machine    MB K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU  /sec %CPU
       1* 100 20254 99.3 110095 55.9 15722  6.1 17901 99.5 601185 99.8 28675.5 100.4
              -------Sequential Output-------- ---Sequential Input-- --Random--
              -Per Char- --Block--- -Rewrite-- -Per Char- --Block--- --Seeks---
Machine    MB K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU  /sec %CPU
       1* 100 18274 88.5 106909 53.2 10614  4.1 18759 99.7 598833 99.4 28461.6 92.5
========
              -------Sequential Output-------- ---Sequential Input-- --Random--
              -Per Char- --Block--- -Rewrite-- -Per Char- --Block--- --Seeks---
Machine    MB K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU  /sec %CPU
       1* 100 15274 98.2 20206  9.7 17286  7.3 18055 99.4 608112 101.0 28424.0 99.5
              -------Sequential Output-------- ---Sequential Input-- --Random--
              -Per Char- --Block--- -Rewrite-- -Per Char- --Block--- --Seeks---
Machine    MB K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU  /sec %CPU
       1* 100 20545 99.1 25332 12.6 16392  6.1 17957 99.4 606706 100.7 27906.8 90.7
              -------Sequential Output-------- ---Sequential Input-- --Random--
              -Per Char- --Block--- -Rewrite-- -Per Char- --Block--- --Seeks---
Machine    MB K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU  /sec %CPU
       1* 100 20482 99.2 30907 13.6 17585  6.2 17867 99.1 608090 101.0 27919.1 97.7
              -------Sequential Output-------- ---Sequential Input-- --Random--
              -Per Char- --Block--- -Rewrite-- -Per Char- --Block--- --Seeks---
Machine    MB K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU  /sec %CPU
       1* 100 20863 99.4 138383 66.2 18945  7.6 17938 99.5 581421 96.5 27094.6 94.8
              -------Sequential Output-------- ---Sequential Input-- --Random--
              -Per Char- --Block--- -Rewrite-- -Per Char- --Block--- --Seeks---
Machine    MB K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU  /sec %CPU
       1* 100 20821 98.8 156821 70.4 11536  4.4 18747 99.0 603556 100.2 27677.8 96.9


And these values (cumulative) result in:

         ACPI		poll
Per Char 95068		97985		+3.06%
Block   291223		371649		+27.62%
Rewrite	67942		81744		+20.31%
Per Char 91357		90564		-0.87%
Block  2979495		3007885		+0.95%
RndSeek	142069.2	139022.3	-2.1%
				average: +8.16%

Now the question is how much is due to idle state entry/exit latency
and how much is due to ACPI idle/wakeup code path execution.

Still, an average of +8.16% during 5 test runs each should be quite some incentive,
and once there's a proper "idle latency skipping during expected I/O replies"
even with idle/wakeup code path reinstated we should hopefully be able to keep
some 5% improvement in disk access.

Andreas Mohr
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