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SubjectRe: Scheduler benchmarks - a follow-up

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

> http://www.healthcarelinen.com/misc/benchmarks/BOUND_hackbench_benchmark2.png

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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