Re: [PATCH] nohz: Revert "nohz: Set isolcpus when nohz_full is set"

From	Thomas Gleixner <tglx@linutronix.de>
Newsgroups	linux.kernel
Subject	Re: [PATCH] nohz: Revert "nohz: Set isolcpus when nohz_full is set"
Date	2015-10-12 22:00 +0200
Message-ID	<qiRqi-A2-9@gated-at.bofh.it> (permalink)
References	<qiNd1-2Xu-41@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Mon, 12 Oct 2015, Frederic Weisbecker wrote:
> This reverts commit 8cb9764fc88b41db11f251e8b2a0d006578b7eb4.
> 
> We assumed that nohz full users always want scheduler isolation on full
> dynticks CPUs, therefore we included nohz full CPUs on cpu_isolated_map.
> This means that tasks run by default on CPUs outside the nohz_full range
> unless their affinity is explicity overwritten.
> 
> This suits pure isolation workloads but when the machine is needed to
> run common workloads, the available sets of CPUs to run common tasks
> becomes reduced.
> 
> We reach an extreme case when CONFIG_NO_HZ_FULL_ALL is enabled as it
> leaves only CPU 0 for non-isolation tasks, which makes people think that
> their supercomputer regressed to 90's UP.
> 
> Some nohz full users appear to be interested in running normal workloads
> either before or after an isolation workload. Nohz full isn't optimized
> toward normal workloads but it's still better than UP performance.
> 
> We are reaching a limitation in kernel presets here. Lets revert this
> cpu_isolated_map inclusion and let userspace do its own scheduler
> isolation using cpusets or explicit affinity settings.

Acked-by: Thomas Gleixner <tglx@linutronix.de>
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[PATCH] nohz: Revert "nohz: Set isolcpus when nohz_full is set" Frederic Weisbecker <fweisbec@gmail.com> - 2015-10-12 17:30 +0200
  Re: [PATCH] nohz: Revert "nohz: Set isolcpus when nohz_full is set" "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-12 17:40 +0200
    Re: [PATCH] nohz: Revert "nohz: Set isolcpus when nohz_full is set" Frederic Weisbecker <fweisbec@gmail.com> - 2015-10-12 18:30 +0200
      Re: [PATCH] nohz: Revert "nohz: Set isolcpus when nohz_full is set" "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-12 19:00 +0200
        Re: [PATCH] nohz: Revert "nohz: Set isolcpus when nohz_full is set" Chris Metcalf <cmetcalf@ezchip.com> - 2015-10-12 19:00 +0200
          Re: [PATCH] nohz: Revert "nohz: Set isolcpus when nohz_full is set" Frederic Weisbecker <fweisbec@gmail.com> - 2015-10-12 19:50 +0200
            Re: [PATCH] nohz: Revert "nohz: Set isolcpus when nohz_full is  set" Christoph Lameter <cl@linux.com> - 2015-10-12 19:50 +0200
              Re: [PATCH] nohz: Revert "nohz: Set isolcpus when nohz_full is set" Frederic Weisbecker <fweisbec@gmail.com> - 2015-10-12 20:00 +0200
              Re: [PATCH] nohz: Revert "nohz: Set isolcpus when nohz_full is set" Frederic Weisbecker <fweisbec@gmail.com> - 2015-10-12 20:00 +0200
                Re: [PATCH] nohz: Revert "nohz: Set isolcpus when nohz_full is set" "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-12 20:30 +0200
                Re: [PATCH] nohz: Revert "nohz: Set isolcpus when nohz_full is  set" Christoph Lameter <cl@linux.com> - 2015-10-12 20:30 +0200
              Re: [PATCH] nohz: Revert "nohz: Set isolcpus when nohz_full is set" "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-12 20:00 +0200
            Re: [PATCH] nohz: Revert "nohz: Set isolcpus when nohz_full is set" Chris Metcalf <cmetcalf@ezchip.com> - 2015-10-12 20:10 +0200
  Re: [PATCH] nohz: Revert "nohz: Set isolcpus when nohz_full is  set" Thomas Gleixner <tglx@linutronix.de> - 2015-10-12 22:00 +0200

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