From: Jacob Keller <jacob.e.keller@intel.com>
To: Thomas Gleixner <tglx@linutronix.de>,
Marcelo Tosatti <mtosatti@redhat.com>
Cc: Nitesh Narayan Lal <nitesh@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
helgaas@kernel.org, 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,
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: Mon, 26 Oct 2020 12:21:45 -0700 [thread overview]
Message-ID: <86f8f667-bda6-59c4-91b7-6ba2ef55e3db@intel.com> (raw)
In-Reply-To: <875z6w4xt4.fsf@nanos.tec.linutronix.de>
On 10/26/2020 12:00 PM, Thomas Gleixner wrote:
> On Mon, Oct 26 2020 at 14:30, Marcelo Tosatti wrote:
>> On Fri, Oct 23, 2020 at 11:00:52PM +0200, Thomas Gleixner wrote:
>>> So without information from the driver which tells what the best number
>>> of interrupts is with a reduced number of CPUs, this cutoff will cause
>>> more problems than it solves. Regressions guaranteed.
>>
>> One might want to move from one interrupt per isolated app core
>> to zero, or vice versa. It seems that "best number of interrupts
>> is with reduced number of CPUs" information, is therefore in userspace,
>> not in driver...
>
> How does userspace know about the driver internals? Number of management
> interrupts, optimal number of interrupts per queue?
>
I guess this is the problem solved in part by the queue management work
that would make queues a thing that userspace is aware of.
Are there drivers which use more than one interrupt per queue? I know
drivers have multiple management interrupts.. and I guess some drivers
do combined 1 interrupt per pair of Tx/Rx.. It's also plausible to to
have multiple queues for one interrupt .. I'm not sure how a single
queue with multiple interrupts would work though.
>>> Managed interrupts base their interrupt allocation and spreading on
>>> information which is handed in by the individual driver and not on crude
>>> assumptions. They are not imposing restrictions on the use case.
>>>
>>> It's perfectly fine for isolated work to save a data set to disk after
>>> computation has finished and that just works with the per-cpu I/O queue
>>> which is otherwise completely silent.
>>
>> Userspace could only change the mask of interrupts which are not
>> triggered by requests from the local CPU (admin, error, mgmt, etc),
>> to avoid the vector exhaustion problem.
>>
>> However, there is no explicit way for userspace to know that, as far as
>> i know.
>>
>> 130: 34845 0 0 0 0 0 0 0 IR-PCI-MSI 33554433-edge nvme0q1
>> 131: 0 27062 0 0 0 0 0 0 IR-PCI-MSI 33554434-edge nvme0q2
>> 132: 0 0 24393 0 0 0 0 0 IR-PCI-MSI 33554435-edge nvme0q3
>> 133: 0 0 0 24313 0 0 0 0 IR-PCI-MSI 33554436-edge nvme0q4
>> 134: 0 0 0 0 20608 0 0 0 IR-PCI-MSI 33554437-edge nvme0q5
>> 135: 0 0 0 0 0 22163 0 0 IR-PCI-MSI 33554438-edge nvme0q6
>> 136: 0 0 0 0 0 0 23020 0 IR-PCI-MSI 33554439-edge nvme0q7
>> 137: 0 0 0 0 0 0 0 24285 IR-PCI-MSI 33554440-edge nvme0q8
>>
>> Can that be retrieved from PCI-MSI information, or drivers
>> have to inform this?
>
> The driver should use a different name for the admin queues.
>
> Thanks,
>
> tglx
>
next prev parent reply other threads:[~2020-10-26 19:22 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 " 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 [this message]
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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