Linux-PCI Archive on lore.kernel.org
 help / color / Atom feed
From: Nitesh Narayan Lal <nitesh@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
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 09:10:41 -0400
Message-ID: <9ee77056-ef02-8696-5b96-46007e35ab00@redhat.com> (raw)
In-Reply-To: <20201023085826.GP2611@hirez.programming.kicks-ass.net>

[-- Attachment #1.1: Type: text/plain, Size: 2123 bytes --]


On 10/23/20 4:58 AM, Peter Zijlstra wrote:
> 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

That make sense.

>
>> 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?
>

Considering we agree that excess vector is a problem that needs to be
solved across all the drivers and that you are comfortable with the other
three patches in the set. If I may suggest the following:

- We can pick those three patches for now, as that will atleast fix a
  driver that is currently impacting RT workloads. Is that a fair
  expectation?

- In the meanwhile, I will start looking into individual drivers that
  consume this API to find out if there is a co-relation that can be
  derived between the max_vecs and number of CPUs. If that exists then I
  can go ahead and tweak the API's max_vecs accordingly. However, if this
  is absolutely random then I can come up with a sane comment
  before this check that covers the list of items you suggested.

- I also want to explore the comments made by Thomas which may take
  some time.


-- 
Thanks
Nitesh


[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

  reply index

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 " 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
2020-10-23 13:10                       ` Nitesh Narayan Lal [this message]
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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=9ee77056-ef02-8696-5b96-46007e35ab00@redhat.com \
    --to=nitesh@redhat.com \
    --cc=bhelgaas@google.com \
    --cc=dennis.dalessandro@intel.com \
    --cc=frederic@kernel.org \
    --cc=hch@infradead.org \
    --cc=helgaas@kernel.org \
    --cc=intel-wired-lan@lists.osuosl.org \
    --cc=jacob.e.keller@intel.com \
    --cc=jeffrey.t.kirsher@intel.com \
    --cc=jesse.brandeburg@intel.com \
    --cc=jiri@nvidia.com \
    --cc=jlelli@redhat.com \
    --cc=juri.lelli@redhat.com \
    --cc=lgoncalv@redhat.com \
    --cc=lihong.yang@intel.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-pci@vger.kernel.org \
    --cc=mike.marciniszyn@intel.com \
    --cc=mingo@redhat.com \
    --cc=mtosatti@redhat.com \
    --cc=netdev@vger.kernel.org \
    --cc=peterz@infradead.org \
    --cc=sassmann@redhat.com \
    --cc=tglx@linutronix.de \
    --cc=thomas.lendacky@amd.com \
    --cc=vincent.guittot@linaro.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-PCI Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-pci/0 linux-pci/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-pci linux-pci/ https://lore.kernel.org/linux-pci \
		linux-pci@vger.kernel.org
	public-inbox-index linux-pci

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-pci


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git