Re: Scheduler benchmarks - a follow-up

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To: Rob Hussey <robjhussey@...>
Cc: <linux-kernel@...>, <ck@...>
Date: Monday, September 17, 2007 - 9:05 am

* Rob Hussey <robjhussey@gmail.com> wrote:


heh - am i the only one impressed by the consistency of the blue line in 
this graph? :-) [ and the green line looks a bit like a .. staircase? ]

i've meanwhile tested hackbench 90 and the performance difference 
between -ck and -cfs-devel seems to be mostly down to the more precise 
(but slower) sched_clock() introduced in v2.6.23 and to the startup 
penalty of freshly created tasks.

Putting back the 2.6.22 version and tweaking the startup penalty gives 
this:

                             [hackbench 90, smaller is better]

            sched-devel.git      sched-devel.git+lowres-sched-clock+dsp
            ---------------      --------------------------------------
                      5.555                  5.149
                      5.641                  5.149
                      5.572                  5.171
                      5.583                  5.155
                      5.532                  5.111
                      5.540                  5.138
                      5.617                  5.176
                      5.542                  5.119
                      5.587                  5.159
                      5.553                  5.177
            --------------------------------------
                 avg: 5.572             avg: 5.150 (-8.1%)

('lowres-sched-clock' is the patch i sent in the previous mail. 'dsp' is 
a disable-startup-penalty patch that is in the latest sched-devel.git)

i have used your .config to conduct this test.

can you reproduce this with the (very-) latest sched-devel git tree:

  git-pull git://git.kernel.org/pub/scm/linux/kernel/git/mingo/linux-2.6-sched-devel.git

plus with the low-res-sched-clock patch (re-) attached below?

	Ingo
---
 arch/i386/kernel/tsc.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Index: linux/arch/i386/kernel/tsc.c
===================================================================
--- linux.orig/arch/i386/kernel/tsc.c
+++ linux/arch/i386/kernel/tsc.c
@@ -110,9 +110,9 @@ unsigned long long native_sched_clock(vo
 	 *   very important for it to be as fast as the platform
 	 *   can achive it. )
 	 */
-	if (unlikely(!tsc_enabled && !tsc_unstable))
+	if (1 || unlikely(!tsc_enabled && !tsc_unstable))
 		/* No locking but a rare wrong value is not a big deal: */
-		return (jiffies_64 - INITIAL_JIFFIES) * (1000000000 / HZ);
+		return jiffies_64 * (1000000000 / HZ);
 
 	/* read the Time Stamp Counter: */
 	rdtscll(this_offset);
-
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Messages in current thread:
Scheduler benchmarks - a follow-up, Rob Hussey, (Mon Sep 17, 5:21 am)
Re: Scheduler benchmarks - a follow-up, Ingo Molnar, (Mon Sep 17, 9:05 am)
Re: Scheduler benchmarks - a follow-up, Rob Hussey, (Mon Sep 17, 9:44 pm)
Re: Scheduler benchmarks - a follow-up, Ingo Molnar, (Mon Sep 17, 4:36 pm)
Re: Scheduler benchmarks - a follow-up, Rob Hussey, (Tue Sep 18, 12:30 am)
Re: Scheduler benchmarks - a follow-up, Ingo Molnar, (Tue Sep 18, 4:48 am)
Re: Scheduler benchmarks - a follow-up, Rob Hussey, (Tue Sep 18, 5:45 am)
Re: Scheduler benchmarks - a follow-up, Ingo Molnar, (Tue Sep 18, 5:48 am)
Re: Scheduler benchmarks - a follow-up, Ingo Molnar, (Tue Sep 18, 2:40 am)
Re: Scheduler benchmarks - a follow-up, Rob Hussey, (Tue Sep 18, 4:23 am)
Re: Scheduler benchmarks - a follow-up, Willy Tarreau, (Tue Sep 18, 12:53 am)
Re: Scheduler benchmarks - a follow-up, Rob Hussey, (Tue Sep 18, 12:58 am)
Re: [ck] Re: Scheduler benchmarks - a follow-up, Jos Poortvliet, (Mon Sep 17, 10:01 am)
Re: [ck] Re: Scheduler benchmarks - a follow-up, Ingo Molnar, (Mon Sep 17, 10:12 am)
Re: Scheduler benchmarks - a follow-up, Ingo Molnar, (Mon Sep 17, 7:27 am)
Re: Scheduler benchmarks - a follow-up, Ed Tomlinson, (Mon Sep 17, 7:12 am)
Re: Scheduler benchmarks - a follow-up, Ingo Molnar, (Mon Sep 17, 4:22 pm)
Re: Scheduler benchmarks - a follow-up, Ingo Molnar, (Mon Sep 17, 7:47 am)