Re: [RFC PATCH 0/3] CFS idle injection

From: Eduardo Valentin <edubezval@gmail.com>
To: Jacob Pan <jacob.jun.pan@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	LKML <linux-kernel@vger.kernel.org>,
	Arjan van de Ven <arjan@linux.intel.com>,
	Paul Turner <pjt@google.com>, Len Brown <len.brown@intel.com>,
	Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
	Tim Chen <tim.c.chen@linux.intel.com>,
	Andi Kleen <andi.kleen@intel.com>,
	Rafael Wysocki <rafael.j.wysocki@intel.com>
Subject: Re: [RFC PATCH 0/3] CFS idle injection
Date: Tue, 3 Nov 2015 22:06:55 -0800	[thread overview]
Message-ID: <20151104060654.GC8850@localhost.localdomain> (raw)
In-Reply-To: <1446509428-5616-1-git-send-email-jacob.jun.pan@linux.intel.com>

Hello Jacob,

On Mon, Nov 02, 2015 at 04:10:25PM -0800, Jacob Pan wrote:
> Hi Peter and all,
> 
> A while ago, we had discussion about how powerclamp is broken in the
> sense of turning off idle ticks in the forced idle period.
> https://lkml.org/lkml/2014/12/18/369
> 
> It was suggested to replace the current kthread play idle loop with a
> timer based runqueue throttling scheme. I finally got around to implement
> this and code is much simpler. I also have good test results in terms of
> efficiency, scalability, etc.
> http://events.linuxfoundation.org/sites/events/files/slides/LinuxCon_Japan_2015_idle_injection1_0.pdf
> slide #18+ shows the data on client and server.
> 
> I have two choices for this code:
> 1) be part of existing powerclamp driver but require exporting some
>    sched APIs.
> 2) be part of sched since the genernal rule applies when it comes down
>    to sycnhronized idle time for best power savings.
> 
> The patches below are for #2. There is a known problem with LOW RES timer
> mode that I am working on. But I am hoping to get review earlier.
> 

I also like #2 too. Specially now that it is not limited to a specific
platform. One question though, could you still keep the cooling device
support of it? In some systems, it might make sense to enable / disable
idle injections based on temperature.

Was there any particular reason you dropped the cooling device support?

BR,

Eduardo Valentin

> We are entering a very power limited environment on client side, frequency
> scaling can only be efficient at certain range. e.g. on SKL, upto ~900MHz,
> anything below, it is increasingly more efficient to do C-states insertion
> if coordinated.
> 
> Looking forward, there are use case beyond thermal/power capping. I think
> we can consolidate ballanced partial busy workload that are evenly
> distributed among CPUs.
> 
> Please let me know what you think.
> 
> Thanks,
> 
> 
> Jacob Pan (3):
>   ktime: add a roundup function
>   timer: relax tick stop in idle entry
>   sched: introduce synchronized idle injection
> 
>  include/linux/ktime.h        |  10 ++
>  include/linux/sched.h        |  12 ++
>  include/linux/sched/sysctl.h |   5 +
>  include/trace/events/sched.h |  23 +++
>  init/Kconfig                 |   8 +
>  kernel/sched/fair.c          | 345 +++++++++++++++++++++++++++++++++++++++++++
>  kernel/sched/sched.h         |   3 +
>  kernel/sysctl.c              |  20 +++
>  kernel/time/tick-sched.c     |   2 +-
>  9 files changed, 427 insertions(+), 1 deletion(-)
> 
> -- 
> 1.9.1
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/