Re: [PATCH v6 5/9] x86/sysctl: Add sysctl for ITMT scheduling feature

From	Thomas Gleixner <tglx@linutronix.de>
Newsgroups	linux.kernel
Subject	Re: [PATCH v6 5/9] x86/sysctl: Add sysctl for ITMT scheduling feature
Date	2016-10-26 13:30 +0200
Message-ID	<swuz7-2VL-13@gated-at.bofh.it> (permalink)
References	<sutHb-52m-11@gated-at.bofh.it> <sutHc-52m-25@gated-at.bofh.it> <swu66-2w2-35@gated-at.bofh.it> <swuz7-2VL-15@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Wed, 26 Oct 2016, Peter Zijlstra wrote:
> On Wed, Oct 26, 2016 at 12:49:36PM +0200, Thomas Gleixner wrote:
> 
> > > +	/*
> > > +	 * ITMT capability automatically enables ITMT
> > > +	 * scheduling for small systems (single node).
> > > +	 */
> > > +	if (topology_num_packages() == 1)
> > > +		sysctl_sched_itmt_enabled = 1;
> > 
> > I really hate this. This is policy and the kernel should not impose
> > policy. Why would I like to have this enforced on my single socket XEON
> > server?
> 
> So this really wants to be enabled by default; otherwise nobody will use
> this, and it really does help single threaded workloads.

Fair enough. Then this wants to be documented.
 
> There were reservations on the multi-socket case of ITMT, maybe it would
> help to spell those out in great detail here. That is, have the comment
> explain the policy instead of simply stating what the code does (which
> is always bad comment policy, you can read the code just fine).

What is the objection for multi sockets? If it improves the behaviour then
why would this be a bad thing for multi sockets?

Thanks,

	tglx

Thread

[PATCH v6 0/9] Support Intel® Turbo Boost Max Technology 3.0 Tim Chen <tim.c.chen@linux.intel.com> - 2016-10-21 00:10 +0200
  [PATCH v6 8/9] acpi: bus: Set _OSC for diverse core support Tim Chen <tim.c.chen@linux.intel.com> - 2016-10-21 00:10 +0200
  [PATCH v6 2/9] x86/topology: Provide topology_num_packages() Tim Chen <tim.c.chen@linux.intel.com> - 2016-10-21 00:10 +0200
  [PATCH v6 4/9] x86: Enable Intel Turbo Boost Max Technology 3.0 Tim Chen <tim.c.chen@linux.intel.com> - 2016-10-21 00:10 +0200
  [PATCH v6 3/9] x86/topology: Define x86's arch_update_cpu_topology Tim Chen <tim.c.chen@linux.intel.com> - 2016-10-21 00:10 +0200
  [PATCH v6 5/9] x86/sysctl: Add sysctl for ITMT scheduling feature Tim Chen <tim.c.chen@linux.intel.com> - 2016-10-21 00:10 +0200
    Re: [PATCH v6 5/9] x86/sysctl: Add sysctl for ITMT scheduling  feature Thomas Gleixner <tglx@linutronix.de> - 2016-10-26 13:00 +0200
      Re: [PATCH v6 5/9] x86/sysctl: Add sysctl for ITMT scheduling  feature Tim Chen <tim.c.chen@linux.intel.com> - 2016-10-26 20:10 +0200
        Re: [PATCH v6 5/9] x86/sysctl: Add sysctl for ITMT scheduling  feature Thomas Gleixner <tglx@linutronix.de> - 2016-10-26 20:20 +0200
          Re: [PATCH v6 5/9] x86/sysctl: Add sysctl for ITMT scheduling  feature Tim Chen <tim.c.chen@linux.intel.com> - 2016-10-26 21:40 +0200
    Re: [PATCH v6 5/9] x86/sysctl: Add sysctl for ITMT scheduling  feature Thomas Gleixner <tglx@linutronix.de> - 2016-10-26 13:00 +0200
      Re: [PATCH v6 5/9] x86/sysctl: Add sysctl for ITMT scheduling  feature Thomas Gleixner <tglx@linutronix.de> - 2016-10-26 13:30 +0200
        Re: [PATCH v6 5/9] x86/sysctl: Add sysctl for ITMT scheduling  feature Tim Chen <tim.c.chen@linux.intel.com> - 2016-10-26 19:30 +0200
          Re: [PATCH v6 5/9] x86/sysctl: Add sysctl for ITMT scheduling  feature Thomas Gleixner <tglx@linutronix.de> - 2016-10-26 20:20 +0200
      Re: [PATCH v6 5/9] x86/sysctl: Add sysctl for ITMT scheduling feature Peter Zijlstra <peterz@infradead.org> - 2016-10-26 13:30 +0200
      Re: [PATCH v6 5/9] x86/sysctl: Add sysctl for ITMT scheduling  feature Tim Chen <tim.c.chen@linux.intel.com> - 2016-10-26 20:10 +0200
  [PATCH v6 1/9] sched: Extend scheduler's asym packing Tim Chen <tim.c.chen@linux.intel.com> - 2016-10-21 00:10 +0200
    Re: [PATCH v6 1/9] sched: Extend scheduler's asym packing Thomas Gleixner <tglx@linutronix.de> - 2016-10-26 12:40 +0200
      Re: [PATCH v6 1/9] sched: Extend scheduler's asym packing Tim Chen <tim.c.chen@linux.intel.com> - 2016-10-26 20:20 +0200
        Re: [PATCH v6 1/9] sched: Extend scheduler's asym packing Thomas Gleixner <tglx@linutronix.de> - 2016-10-26 20:30 +0200
  [PATCH v6 7/9] acpi: bus: Enable HWP CPPC objects Tim Chen <tim.c.chen@linux.intel.com> - 2016-10-21 00:10 +0200
  [PATCH v6 9/9] cpufreq: intel_pstate: Use CPPC to get max performance Tim Chen <tim.c.chen@linux.intel.com> - 2016-10-21 00:10 +0200
  [PATCH v6 6/9] x86/sched: Add SD_ASYM_PACKING flags to x86 ITMT CPU Tim Chen <tim.c.chen@linux.intel.com> - 2016-10-21 00:10 +0200

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