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From: Peter Zijlstra <peterz@infradead.org>
To: Nitesh Narayan Lal <nitesh@redhat.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>,
	helgaas@kernel.org, Thomas Gleixner <tglx@linutronix.de>,
	linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
	linux-pci@vger.kernel.org, intel-wired-lan@lists.osuosl.org,
	frederic@kernel.org, sassmann@redhat.com,
	jesse.brandeburg@intel.com, lihong.yang@intel.com,
	jeffrey.t.kirsher@intel.com, jacob.e.keller@intel.com,
	jlelli@redhat.com, hch@infradead.org, bhelgaas@google.com,
	mike.marciniszyn@intel.com, dennis.dalessandro@intel.com,
	thomas.lendacky@amd.com, jiri@nvidia.com, mingo@redhat.com,
	juri.lelli@redhat.com, vincent.guittot@linaro.org,
	lgoncalv@redhat.com
Subject: Re: [PATCH v4 4/4] PCI: Limit pci_alloc_irq_vectors() to housekeeping CPUs
Date: Fri, 23 Oct 2020 10:58:26 +0200	[thread overview]
Message-ID: <20201023085826.GP2611@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <260f4191-5b9f-6dc1-9f11-085533ac4f55@redhat.com>

On Thu, Oct 22, 2020 at 01:47:14PM -0400, Nitesh Narayan Lal wrote:

> Hi Peter,
> 
> So based on the suggestions from you and Thomas, I think something like the
> following should do the job within pci_alloc_irq_vectors_affinity():
> 
> +       if (!pci_is_managed(dev) && (hk_cpus < num_online_cpus()))
> +               max_vecs = clamp(hk_cpus, min_vecs, max_vecs);
> 
> I do know that you didn't like the usage of "hk_cpus < num_online_cpus()"
> and to an extent I agree that it does degrade the code clarity.

It's not just code clarity; I simply don't understand it. It feels like
a band-aid that breaks thing.

At the very least it needs a ginormous (and coherent) comment that
explains:

 - the interface
 - the usage
 - this hack

> However, since there is a certain inconsistency in the number of vectors
> that drivers request through this API IMHO we will need this, otherwise
> we could cause an impact on the drivers even in setups that doesn't
> have any isolated CPUs.

So shouldn't we then fix the drivers / interface first, to get rid of
this inconsistency?

> If you agree, I can send the next version of the patch-set.

Well, it's not just me you have to convince.

  reply	other threads:[~2020-10-23  8:58 UTC|newest]

Thread overview: 55+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-28 18:35 [PATCH v4 0/4] isolation: limit msix vectors to housekeeping CPUs Nitesh Narayan Lal
2020-09-28 18:35 ` [PATCH v4 1/4] sched/isolation: API to get number of " Nitesh Narayan Lal
2020-09-28 18:35 ` [PATCH v4 2/4] sched/isolation: Extend nohz_full to isolate managed IRQs Nitesh Narayan Lal
2020-10-23 13:25   ` Peter Zijlstra
2020-10-23 13:29     ` Frederic Weisbecker
2020-10-23 13:57       ` Nitesh Narayan Lal
2020-10-23 13:45     ` Nitesh Narayan Lal
2020-09-28 18:35 ` [PATCH v4 3/4] i40e: Limit msix vectors to housekeeping CPUs Nitesh Narayan Lal
2020-09-28 18:35 ` [PATCH v4 4/4] PCI: Limit pci_alloc_irq_vectors() " Nitesh Narayan Lal
2020-09-28 21:59   ` Bjorn Helgaas
2020-09-29 17:46     ` Christoph Hellwig
2020-10-16 12:20   ` Peter Zijlstra
2020-10-18 18:14     ` Nitesh Narayan Lal
2020-10-19 11:11       ` Peter Zijlstra
2020-10-19 14:00         ` Marcelo Tosatti
2020-10-19 14:25           ` Nitesh Narayan Lal
2020-10-20  7:30           ` Peter Zijlstra
2020-10-20 13:00             ` Nitesh Narayan Lal
2020-10-20 13:41               ` Peter Zijlstra
2020-10-20 14:39                 ` Nitesh Narayan Lal
2020-10-22 17:47                   ` Nitesh Narayan Lal
2020-10-23  8:58                     ` Peter Zijlstra [this message]
2020-10-23 13:10                       ` Nitesh Narayan Lal
2020-10-23 21:00                         ` Thomas Gleixner
2020-10-26 13:35                           ` Nitesh Narayan Lal
2020-10-26 13:57                             ` Thomas Gleixner
2020-10-26 17:30                           ` Marcelo Tosatti
2020-10-26 19:00                             ` Thomas Gleixner
2020-10-26 19:11                               ` Marcelo Tosatti
2020-10-26 19:21                               ` Jacob Keller
2020-10-26 20:11                                 ` Thomas Gleixner
2020-10-26 21:11                                   ` Jacob Keller
2020-10-26 21:50                                     ` Thomas Gleixner
2020-10-26 22:13                                       ` Jakub Kicinski
2020-10-26 22:46                                         ` Thomas Gleixner
2020-10-26 22:52                                         ` Jacob Keller
2020-10-26 22:22                                       ` Nitesh Narayan Lal
2020-10-26 22:49                                         ` Thomas Gleixner
2020-10-26 23:08                                           ` Jacob Keller
2020-10-27 14:28                                             ` Thomas Gleixner
2020-10-27 11:47                                         ` Marcelo Tosatti
2020-10-27 14:43                                           ` Thomas Gleixner
2020-10-19 14:21         ` Frederic Weisbecker
2020-10-20 14:16   ` Thomas Gleixner
2020-10-20 16:18     ` Nitesh Narayan Lal
2020-10-20 18:07       ` Thomas Gleixner
2020-10-21 20:25         ` Thomas Gleixner
2020-10-21 21:04           ` Nitesh Narayan Lal
2020-10-22  0:02           ` Jakub Kicinski
2020-10-22  0:27             ` Jacob Keller
2020-10-22  8:28             ` Thomas Gleixner
2020-10-22 12:28           ` Marcelo Tosatti
2020-10-22 22:39             ` Thomas Gleixner
2020-10-01 15:49 ` [PATCH v4 0/4] isolation: limit msix vectors " Frederic Weisbecker
2020-10-08 21:40   ` Nitesh Narayan Lal

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