From: Tim Chen <tim.c.chen@linux.intel.com>
To: Thomas Gleixner <tglx@linutronix.de>,
Peter Zijlstra <peterz@infradead.org>
Cc: rjw@rjwysocki.net, mingo@redhat.com, bp@suse.de, x86@kernel.org,
linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-acpi@vger.kernel.org, jolsa@redhat.com,
Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Subject: Re: [PATCH v6 5/9] x86/sysctl: Add sysctl for ITMT scheduling feature
Date: Wed, 26 Oct 2016 10:23:32 -0700 [thread overview]
Message-ID: <1477502612.2680.9.camel@linux.intel.com> (raw)
In-Reply-To: <alpine.DEB.2.20.1610261322580.4983@nanos>
On Wed, 2016-10-26 at 13:24 +0200, Thomas Gleixner wrote:
> 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?
For multi-socket (server system), it is much more likely that they will
have multiple cpus in a socket busy and not run in turbo mode. So the extra
work in migrating the workload to the one with extra headroom will
not make use of those headroom in that scenario. I will update the comment
to reflect this policy.
See also our previous discussions: http://lkml.iu.edu/hypermail/linux/kernel/1609.1/03381.html
Tim
next prev parent reply other threads:[~2016-10-26 17:23 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-10-20 21:59 [PATCH v6 0/9] Support Intel® Turbo Boost Max Technology 3.0 Tim Chen
2016-10-20 21:59 ` [PATCH v6 1/9] sched: Extend scheduler's asym packing Tim Chen
2016-10-26 10:27 ` Thomas Gleixner
2016-10-26 18:10 ` Tim Chen
2016-10-26 18:23 ` Thomas Gleixner
2016-10-20 21:59 ` [PATCH v6 2/9] x86/topology: Provide topology_num_packages() Tim Chen
2016-10-20 21:59 ` [PATCH v6 3/9] x86/topology: Define x86's arch_update_cpu_topology Tim Chen
2016-10-20 21:59 ` [PATCH v6 4/9] x86: Enable Intel Turbo Boost Max Technology 3.0 Tim Chen
2016-10-20 21:59 ` [PATCH v6 5/9] x86/sysctl: Add sysctl for ITMT scheduling feature Tim Chen
2016-10-26 10:49 ` Thomas Gleixner
2016-10-26 11:25 ` Peter Zijlstra
2016-10-26 11:24 ` Thomas Gleixner
2016-10-26 17:23 ` Tim Chen [this message]
2016-10-26 18:09 ` Thomas Gleixner
2016-10-27 19:32 ` Tim Chen
2016-10-26 17:59 ` Tim Chen
2016-10-26 10:52 ` Thomas Gleixner
2016-10-26 18:03 ` Tim Chen
2016-10-26 18:11 ` Thomas Gleixner
2016-10-26 19:38 ` Tim Chen
2016-10-20 22:00 ` [PATCH v6 6/9] x86/sched: Add SD_ASYM_PACKING flags to x86 ITMT CPU Tim Chen
2016-10-20 22:00 ` [PATCH v6 7/9] acpi: bus: Enable HWP CPPC objects Tim Chen
2016-10-20 22:00 ` [PATCH v6 8/9] acpi: bus: Set _OSC for diverse core support Tim Chen
2016-10-20 22:00 ` [PATCH v6 9/9] cpufreq: intel_pstate: Use CPPC to get max performance Tim Chen
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