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From: Frederic Weisbecker <frederic@kernel.org>
To: Jesse Brandeburg <jesse.brandeburg@intel.com>
Cc: Nitesh Narayan Lal <nitesh@redhat.com>,
	linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
	linux-pci@vger.kernel.org, mtosatti@redhat.com,
	sassmann@redhat.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,
	jerinj@marvell.com, mathias.nyman@intel.com, jiri@nvidia.com
Subject: Re: [RFC][Patch v1 2/3] i40e: limit msix vectors based on housekeeping CPUs
Date: Tue, 22 Sep 2020 00:58:35 +0200	[thread overview]
Message-ID: <20200921225834.GA30521@lenoir> (raw)
In-Reply-To: <20200917112359.00006e10@intel.com>

On Thu, Sep 17, 2020 at 11:23:59AM -0700, Jesse Brandeburg wrote:
> Nitesh Narayan Lal wrote:
> 
> > In a realtime environment, it is essential to isolate unwanted IRQs from
> > isolated CPUs to prevent latency overheads. Creating MSIX vectors only
> > based on the online CPUs could lead to a potential issue on an RT setup
> > that has several isolated CPUs but a very few housekeeping CPUs. This is
> > because in these kinds of setups an attempt to move the IRQs to the
> > limited housekeeping CPUs from isolated CPUs might fail due to the per
> > CPU vector limit. This could eventually result in latency spikes because
> > of the IRQ threads that we fail to move from isolated CPUs.
> > 
> > This patch prevents i40e to add vectors only based on available
> > housekeeping CPUs by using num_housekeeping_cpus().
> > 
> > Signed-off-by: Nitesh Narayan Lal <nitesh@redhat.com>
> 
> The driver changes are straightforward, but this isn't the only driver
> with this issue, right?  I'm sure ixgbe and ice both have this problem
> too, you should fix them as well, at a minimum, and probably other
> vendors drivers:
> 
> $ rg -c --stats num_online_cpus drivers/net/ethernet
> ...
> 50 files contained matches

Ouch, I was indeed surprised that these MSI vector allocations were done
at the driver level and not at some $SUBSYSTEM level.

The logic is already there in the driver so I wouldn't oppose to this very patch
but would a shared infrastructure make sense for this? Something that would
also handle hotplug operations?

Does it possibly go even beyond networking drivers?

Thanks.

> 
> for this patch i40e
> Acked-by: Jesse Brandeburg <jesse.brandeburg@intel.com>

  parent reply	other threads:[~2020-09-21 22:58 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-09 15:08 [RFC] [PATCH v1 0/3] isolation: limit msix vectors based on housekeeping CPUs Nitesh Narayan Lal
2020-09-09 15:08 ` [RFC][Patch v1 1/3] sched/isolation: API to get num of hosekeeping CPUs Nitesh Narayan Lal
2020-09-17 18:18   ` Jesse Brandeburg
2020-09-17 18:43     ` Nitesh Narayan Lal
2020-09-17 20:11   ` Bjorn Helgaas
2020-09-17 21:48     ` Jacob Keller
2020-09-17 22:09     ` Nitesh Narayan Lal
2020-09-21 23:40   ` Frederic Weisbecker
2020-09-22  3:16     ` Nitesh Narayan Lal
2020-09-22 10:08       ` Frederic Weisbecker
2020-09-22 13:50         ` Nitesh Narayan Lal
2020-09-22 20:58           ` Frederic Weisbecker
2020-09-22 21:15             ` Nitesh Narayan Lal
2020-09-22 21:26             ` Andrew Lunn
2020-09-22 22:20               ` Nitesh Narayan Lal
2020-09-09 15:08 ` [RFC][Patch v1 2/3] i40e: limit msix vectors based on housekeeping CPUs Nitesh Narayan Lal
2020-09-11 15:23   ` Marcelo Tosatti
2020-09-17 18:23   ` Jesse Brandeburg
2020-09-17 18:31     ` Nitesh Narayan Lal
2020-09-21 22:58     ` Frederic Weisbecker [this message]
2020-09-22  3:08       ` Nitesh Narayan Lal
2020-09-22  9:54         ` Frederic Weisbecker
2020-09-22 13:34           ` Nitesh Narayan Lal
2020-09-22 20:44             ` Frederic Weisbecker
2020-09-22 21:05               ` Nitesh Narayan Lal
2020-09-09 15:08 ` [RFC][Patch v1 3/3] PCI: Limit pci_alloc_irq_vectors as per " Nitesh Narayan Lal
2020-09-10 19:22   ` Marcelo Tosatti
2020-09-10 19:31     ` Nitesh Narayan Lal
2020-09-22 13:54       ` Nitesh Narayan Lal
2020-09-22 21:08         ` Frederic Weisbecker

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