Re: [PATCH 2/2] sched,time: call __acct_update_integrals once a jiffy

[Mike Galbraith]

On Sat, 2016-01-30 at 15:20 +0100, Frederic Weisbecker wrote:
> On Fri, Jan 29, 2016 at 05:43:28PM -0500, Rik van Riel wrote:

> > Run times for the microbenchmark:
> > 
> > 4.4                             3.8 seconds
> > 4.5-rc1                         3.7 seconds
> > 4.5-rc1 + first patch           3.3 seconds
> > 4.5-rc1 + both patches          2.3 seconds
> 
> Very nice improvement!

Tasty indeed.

When nohz_full CPUs are not isolated, ie are being used as generic
CPUs, get_nohz_timer_target() is a problem with things like tbench.

tbench 8 with Rik's patches applied:
nohz_full=empty
Throughput 3204.69 MB/sec  1.000
nohz_full=1-3,5-7 
Throughput 1354.99 MB/sec   .422  1.000
nohz_full=1-3,5-7 + club below 
Throughput 2762.22 MB/sec   .861  2.038

With Rik's patches and a club, tbench becomes nearly acceptable.
---
 include/linux/tick.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/include/linux/tick.h
+++ b/include/linux/tick.h
@@ -184,7 +184,7 @@ static inline const struct cpumask *hous
 static inline bool is_housekeeping_cpu(int cpu)
 {
 #ifdef CONFIG_NO_HZ_FULL
-	if (tick_nohz_full_enabled())
+	if (tick_nohz_full_enabled() && runqueue_is_isolated(cpu))
 		return cpumask_test_cpu(cpu, housekeeping_mask);
 #endif
 	return true;