Messages in this thread | | | Date | Mon, 24 Aug 2009 21:10:13 +0530 | From | Vaidyanathan Srinivasan <> | Subject | Re: [PATCH 10/15] sched: Check for sched_mn_power_savings when doing load balancing |
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* Peter Zijlstra <peterz@infradead.org> [2009-08-24 17:03:40]:
> On Thu, 2009-08-20 at 15:41 +0200, Andreas Herrmann wrote: > > The patch adds support for POWERSAVINGS_BALANCE_BASIC for MN domain > > level. Currently POWERSAVINGS_BALANCE_WAKEUP is not used for MN domain. > > > > (I have to admit that so far I don't have the correct understanding > > what's the benefit of POWERSAVINGS_BALANCE_WAKEUP (when an deticated > > wakeup CPU is used) in contrast to POWERSAVINGS_BALANCE_BASIC. I also > > have not found an example that would demonstrate the difference > > between those two powersaving levels.) > > blame svaidy for not writing enough comments ;-)
I am here to explain ;)
> iirc it moves tasks to sched_mv_preferred_wakeup_cpu instead of waking > an idle cpu, this leaves idle cpus idle longer at the cost of creating > overload on other cpus.
Yes, as Peter said, the POWERSAVINGS_BALANCE_WAKEUP biases task wakeups to sched_mc_preferred_wakeup_cpu which has been nominated from previous load balance loops.
Task wakeup biasing of sched_mc=2 works for most workloads like kernbench and other sleeping tasks that come in and out of runqueue. The default sched_mc=1 will work only for jobs running much longer than the loadbalance interval or almost 100% CPU intensive job where the load balancer can take time to identify the load pattern and initiate a task migrate.
The wakeup biasing (sched_mc=2) will help move bursty jobs faster and statistically pack them in single package and save power.
> > Signed-off-by: Andreas Herrmann <andreas.herrmann3@amd.com> > > --- > > kernel/sched.c | 5 +++-- > > 1 files changed, 3 insertions(+), 2 deletions(-) > > > > diff --git a/kernel/sched.c b/kernel/sched.c > > index ebcda58..7a0d710 100644 > > --- a/kernel/sched.c > > +++ b/kernel/sched.c > > @@ -4591,7 +4591,8 @@ static int find_new_ilb(int cpu) > > * Have idle load balancer selection from semi-idle packages only > > * when power-aware load balancing is enabled > > */ > > - if (!(sched_smt_power_savings || sched_mc_power_savings)) > > + if (!(sched_smt_power_savings || sched_mc_power_savings || > > + sched_mn_power_savings)) > > goto out_done; > > > > /* > > @@ -4681,7 +4682,7 @@ int select_nohz_load_balancer(int stop_tick) > > int new_ilb; > > > > if (!(sched_smt_power_savings || > > - sched_mc_power_savings)) > > + sched_mc_power_savings || sched_mn_power_savings)) > > return 1; > > /* > > * Check to see if there is a more power-efficient
You can achieve the balancing effects by propagating the SD_ flags at the right domain level with the same sysfs interface. At some point we wanted to change to sched_power_savings=N and set the flags according to system topology to provide consolidation at the right sched_domain and save power.
--Vaidy
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