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Date: Fri, 23 Oct 2020 10:58:26 +0200 From: Peter Zijlstra <peterz@...radead.org> To: Nitesh Narayan Lal <nitesh@...hat.com> Cc: Marcelo Tosatti <mtosatti@...hat.com>, helgaas@...nel.org, Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org, netdev@...r.kernel.org, linux-pci@...r.kernel.org, intel-wired-lan@...ts.osuosl.org, frederic@...nel.org, sassmann@...hat.com, jesse.brandeburg@...el.com, lihong.yang@...el.com, jeffrey.t.kirsher@...el.com, jacob.e.keller@...el.com, jlelli@...hat.com, hch@...radead.org, bhelgaas@...gle.com, mike.marciniszyn@...el.com, dennis.dalessandro@...el.com, thomas.lendacky@....com, jiri@...dia.com, mingo@...hat.com, juri.lelli@...hat.com, vincent.guittot@...aro.org, lgoncalv@...hat.com Subject: Re: [PATCH v4 4/4] PCI: Limit pci_alloc_irq_vectors() to housekeeping CPUs 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.
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