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From: Jacob Keller <jacob.e.keller@intel.com>
To: Bjorn Helgaas <helgaas@kernel.org>,
	Nitesh Narayan Lal <nitesh@redhat.com>
Cc: linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
	linux-pci@vger.kernel.org, frederic@kernel.org,
	mtosatti@redhat.com, sassmann@redhat.com,
	jeffrey.t.kirsher@intel.com, jlelli@redhat.com,
	hch@infradead.org, bhelgaas@google.com,
	mike.marciniszyn@intel.com, dennis.dalessandro@intel.com,
	thomas.lendacky@amd.com, jerinj@marvell.com,
	mathias.nyman@intel.com, jiri@nvidia.com,
	Ingo Molnar <mingo@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Juri Lelli <juri.lelli@redhat.com>,
	Vincent Guittot <vincent.guittot@linaro.org>
Subject: Re: [RFC][Patch v1 1/3] sched/isolation: API to get num of hosekeeping CPUs
Date: Thu, 17 Sep 2020 14:48:30 -0700	[thread overview]
Message-ID: <238f4d32-ac26-e0c6-b53c-9f7ab98050ca@intel.com> (raw)
In-Reply-To: <20200917201123.GA1726926@bjorn-Precision-5520>



On 9/17/2020 1:11 PM, Bjorn Helgaas wrote:
> [+cc Ingo, Peter, Juri, Vincent (scheduler maintainers)]
> 
> s/hosekeeping/housekeeping/ (in subject)
> 
> On Wed, Sep 09, 2020 at 11:08:16AM -0400, Nitesh Narayan Lal wrote:
>> Introduce a new API num_housekeeping_cpus(), that can be used to retrieve
>> the number of housekeeping CPUs by reading an atomic variable
>> __num_housekeeping_cpus. This variable is set from housekeeping_setup().
>>
>> This API is introduced for the purpose of drivers that were previously
>> relying only on num_online_cpus() to determine the number of MSIX vectors
>> to create. In an RT environment with large isolated but a fewer
>> housekeeping CPUs this was leading to a situation where an attempt to
>> move all of the vectors corresponding to isolated CPUs to housekeeping
>> CPUs was failing due to per CPU vector limit.
> 
> Totally kibitzing here, but AFAICT the concepts of "isolated CPU" and
> "housekeeping CPU" are not currently exposed to drivers, and it's not
> completely clear to me that they should be.
> 
> We have carefully constructed notions of possible, present, online,
> active CPUs, and it seems like whatever we do here should be
> somehow integrated with those.
> 

Perhaps "active" CPUs could be separated to not include the isolated CPUs?

  reply	other threads:[~2020-09-17 21:55 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-09 15:08 [RFC] [PATCH v1 0/3] isolation: limit msix vectors based on housekeeping CPUs Nitesh Narayan Lal
2020-09-09 15:08 ` [RFC][Patch v1 1/3] sched/isolation: API to get num of hosekeeping CPUs Nitesh Narayan Lal
2020-09-17 18:18   ` Jesse Brandeburg
2020-09-17 18:43     ` Nitesh Narayan Lal
2020-09-17 20:11   ` Bjorn Helgaas
2020-09-17 21:48     ` Jacob Keller [this message]
2020-09-17 22:09     ` Nitesh Narayan Lal
2020-09-21 23:40   ` Frederic Weisbecker
2020-09-22  3:16     ` Nitesh Narayan Lal
2020-09-22 10:08       ` Frederic Weisbecker
2020-09-22 13:50         ` Nitesh Narayan Lal
2020-09-22 20:58           ` Frederic Weisbecker
2020-09-22 21:15             ` Nitesh Narayan Lal
2020-09-22 21:26             ` Andrew Lunn
2020-09-22 22:20               ` Nitesh Narayan Lal
2020-09-09 15:08 ` [RFC][Patch v1 2/3] i40e: limit msix vectors based on housekeeping CPUs Nitesh Narayan Lal
2020-09-11 15:23   ` Marcelo Tosatti
2020-09-17 18:23   ` Jesse Brandeburg
2020-09-17 18:31     ` Nitesh Narayan Lal
2020-09-21 22:58     ` Frederic Weisbecker
2020-09-22  3:08       ` Nitesh Narayan Lal
2020-09-22  9:54         ` Frederic Weisbecker
2020-09-22 13:34           ` Nitesh Narayan Lal
2020-09-22 20:44             ` Frederic Weisbecker
2020-09-22 21:05               ` Nitesh Narayan Lal
2020-09-09 15:08 ` [RFC][Patch v1 3/3] PCI: Limit pci_alloc_irq_vectors as per " Nitesh Narayan Lal
2020-09-10 19:22   ` Marcelo Tosatti
2020-09-10 19:31     ` Nitesh Narayan Lal
2020-09-22 13:54       ` Nitesh Narayan Lal
2020-09-22 21:08         ` Frederic Weisbecker

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