From: Marcelo Tosatti <mtosatti@redhat.com>
To: Nitesh Narayan Lal <nitesh@redhat.com>
Cc: linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
linux-pci@vger.kernel.org, frederic@kernel.org,
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 3/3] PCI: Limit pci_alloc_irq_vectors as per housekeeping CPUs
Date: Thu, 10 Sep 2020 16:22:08 -0300 [thread overview]
Message-ID: <20200910192208.GA24845@fuller.cnet> (raw)
In-Reply-To: <20200909150818.313699-4-nitesh@redhat.com>
On Wed, Sep 09, 2020 at 11:08:18AM -0400, Nitesh Narayan Lal wrote:
> This patch limits the pci_alloc_irq_vectors max vectors that is passed on
> by the caller based on the available housekeeping CPUs by only using the
> minimum of the two.
>
> A minimum of the max_vecs passed and available housekeeping CPUs is
> derived to ensure that we don't create excess vectors which can be
> problematic specifically in an RT environment. This is because for an RT
> environment unwanted IRQs are moved to the housekeeping CPUs from
> isolated CPUs to keep the latency overhead to a minimum. If the number of
> housekeeping CPUs are significantly lower than that of the isolated CPUs
> we can run into failures while moving these IRQs to housekeeping due to
> per CPU vector limit.
>
> Signed-off-by: Nitesh Narayan Lal <nitesh@redhat.com>
> ---
> include/linux/pci.h | 16 ++++++++++++++++
> 1 file changed, 16 insertions(+)
>
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 835530605c0d..750ba927d963 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -38,6 +38,7 @@
> #include <linux/interrupt.h>
> #include <linux/io.h>
> #include <linux/resource_ext.h>
> +#include <linux/sched/isolation.h>
> #include <uapi/linux/pci.h>
>
> #include <linux/pci_ids.h>
> @@ -1797,6 +1798,21 @@ static inline int
> pci_alloc_irq_vectors(struct pci_dev *dev, unsigned int min_vecs,
> unsigned int max_vecs, unsigned int flags)
> {
> + unsigned int num_housekeeping = num_housekeeping_cpus();
> + unsigned int num_online = num_online_cpus();
> +
> + /*
> + * Try to be conservative and at max only ask for the same number of
> + * vectors as there are housekeeping CPUs. However, skip any
> + * modification to the of max vectors in two conditions:
> + * 1. If the min_vecs requested are higher than that of the
> + * housekeeping CPUs as we don't want to prevent the initialization
> + * of a device.
> + * 2. If there are no isolated CPUs as in this case the driver should
> + * already have taken online CPUs into consideration.
> + */
> + if (min_vecs < num_housekeeping && num_housekeeping != num_online)
> + max_vecs = min_t(int, max_vecs, num_housekeeping);
> return pci_alloc_irq_vectors_affinity(dev, min_vecs, max_vecs, flags,
> NULL);
> }
If min_vecs > num_housekeeping, for example:
/* PCI MSI/MSIx support */
#define XGBE_MSI_BASE_COUNT 4
#define XGBE_MSI_MIN_COUNT (XGBE_MSI_BASE_COUNT + 1)
Then the protection fails.
How about reducing max_vecs down to min_vecs, if min_vecs >
num_housekeeping ?
next prev parent reply other threads:[~2020-09-10 19:23 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
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 [this message]
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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