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From: Thomas Gleixner <tglx@linutronix.de>
To: Jakub Kicinski <kuba@kernel.org>
Cc: Nitesh Narayan Lal <nitesh@redhat.com>,
	linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
	linux-pci@vger.kernel.org, intel-wired-lan@lists.osuosl.org,
	frederic@kernel.org, mtosatti@redhat.com, sassmann@redhat.com,
	jesse.brandeburg@intel.com, lihong.yang@intel.com,
	helgaas@kernel.org, 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, peterz@infradead.org,
	juri.lelli@redhat.com, vincent.guittot@linaro.org,
	lgoncalv@redhat.com, Dave Miller <davem@davemloft.net>,
	Magnus Karlsson <magnus.karlsson@intel.com>,
	Saeed Mahameed <saeedm@nvidia.com>
Subject: Re: [PATCH v4 4/4] PCI: Limit pci_alloc_irq_vectors() to housekeeping CPUs
Date: Thu, 22 Oct 2020 10:28:02 +0200
Message-ID: <874kmm7jhp.fsf@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20201021170224.55aea948@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>

On Wed, Oct 21 2020 at 17:02, Jakub Kicinski wrote:
> On Wed, 21 Oct 2020 22:25:48 +0200 Thomas Gleixner wrote:
>> The right answer to this is to utilize managed interrupts and have
>> according logic in your network driver to handle CPU hotplug. When a CPU
>> goes down, then the queue which is associated to that CPU is quiesced
>> and the interrupt core shuts down the relevant interrupt instead of
>> moving it to an online CPU (which causes the whole vector exhaustion
>> problem on x86). When the CPU comes online again, then the interrupt is
>> reenabled in the core and the driver reactivates the queue.
>
> I think Mellanox folks made some forays into managed irqs, but I don't
> remember/can't find the details now.
>
> For networking the locality / queue per core does not always work,
> since the incoming traffic is usually spread based on a hash. Many

That makes it problematic and is fundamentally different from block I/O.

> applications perform better when network processing is done on a small
> subset of CPUs, and application doesn't get interrupted every 100us. 
> So we do need extra user control here.

Ok.

> We have a bit of a uAPI problem since people had grown to depend on
> IRQ == queue == NAPI to configure their systems. "The right way" out
> would be a proper API which allows associating queues with CPUs rather
> than IRQs, then we can use managed IRQs and solve many other problems.
>
> Such new API has been in the works / discussions for a while now.

If there is anything which needs to be done/extended on the irq side
please let me know.

Thanks

        tglx

  parent 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
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 [this message]
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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