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Date: Mon, 11 Jan 2021 22:25:42 -0500
From: Don Dutile <ddutile@...hat.com>
To: Alexander Duyck <alexander.duyck@...il.com>,
Leon Romanovsky <leon@...nel.org>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>,
Saeed Mahameed <saeedm@...dia.com>,
Leon Romanovsky <leonro@...dia.com>,
Jason Gunthorpe <jgg@...dia.com>,
Jakub Kicinski <kuba@...nel.org>,
linux-pci <linux-pci@...r.kernel.org>,
linux-rdma@...r.kernel.org, Netdev <netdev@...r.kernel.org>,
Alex Williamson <alex.williamson@...hat.com>
Subject: Re: [PATCH mlx5-next v1 1/5] PCI: Add sysfs callback to allow MSI-X
table size change of SR-IOV VFs
On 1/11/21 2:30 PM, Alexander Duyck wrote:
> On Sun, Jan 10, 2021 at 7:12 AM Leon Romanovsky <leon@...nel.org> wrote:
>> From: Leon Romanovsky <leonro@...dia.com>
>>
>> Extend PCI sysfs interface with a new callback that allows configure
>> the number of MSI-X vectors for specific SR-IO VF. This is needed
>> to optimize the performance of newly bound devices by allocating
>> the number of vectors based on the administrator knowledge of targeted VM.
>>
>> This function is applicable for SR-IOV VF because such devices allocate
>> their MSI-X table before they will run on the VMs and HW can't guess the
>> right number of vectors, so the HW allocates them statically and equally.
>>
>> The newly added /sys/bus/pci/devices/.../vf_msix_vec file will be seen
>> for the VFs and it is writable as long as a driver is not bounded to the VF.
>>
>> The values accepted are:
>> * > 0 - this will be number reported by the VF's MSI-X capability
>> * < 0 - not valid
>> * = 0 - will reset to the device default value
>>
>> Signed-off-by: Leon Romanovsky <leonro@...dia.com>
>> ---
>> Documentation/ABI/testing/sysfs-bus-pci | 20 ++++++++
>> drivers/pci/iov.c | 62 +++++++++++++++++++++++++
>> drivers/pci/msi.c | 29 ++++++++++++
>> drivers/pci/pci-sysfs.c | 1 +
>> drivers/pci/pci.h | 2 +
>> include/linux/pci.h | 8 +++-
>> 6 files changed, 121 insertions(+), 1 deletion(-)
>>
>> diff --git a/Documentation/ABI/testing/sysfs-bus-pci b/Documentation/ABI/testing/sysfs-bus-pci
>> index 25c9c39770c6..05e26e5da54e 100644
>> --- a/Documentation/ABI/testing/sysfs-bus-pci
>> +++ b/Documentation/ABI/testing/sysfs-bus-pci
>> @@ -375,3 +375,23 @@ Description:
>> The value comes from the PCI kernel device state and can be one
>> of: "unknown", "error", "D0", D1", "D2", "D3hot", "D3cold".
>> The file is read only.
>> +
>> +What: /sys/bus/pci/devices/.../vf_msix_vec
> So the name for this doesn't seem to match existing SR-IOV naming. It
> seems like this should probably be something like sriov_vf_msix_count
> in order to be closer to the actual naming of what is being dealt
> with.
>
>> +Date: December 2020
>> +Contact: Leon Romanovsky <leonro@...dia.com>
>> +Description:
>> + This file is associated with the SR-IOV VFs.
>> + It allows configuration of the number of MSI-X vectors for
>> + the VF. This is needed to optimize performance of newly bound
>> + devices by allocating the number of vectors based on the
>> + administrator knowledge of targeted VM.
>> +
>> + The values accepted are:
>> + * > 0 - this will be number reported by the VF's MSI-X
>> + capability
>> + * < 0 - not valid
>> + * = 0 - will reset to the device default value
>> +
>> + The file is writable if the PF is bound to a driver that
>> + supports the ->sriov_set_msix_vec_count() callback and there
>> + is no driver bound to the VF.
>> diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
>> index 4afd4ee4f7f0..42c0df4158d1 100644
>> --- a/drivers/pci/iov.c
>> +++ b/drivers/pci/iov.c
>> @@ -31,6 +31,7 @@ int pci_iov_virtfn_devfn(struct pci_dev *dev, int vf_id)
>> return (dev->devfn + dev->sriov->offset +
>> dev->sriov->stride * vf_id) & 0xff;
>> }
>> +EXPORT_SYMBOL(pci_iov_virtfn_devfn);
>>
>> /*
>> * Per SR-IOV spec sec 3.3.10 and 3.3.11, First VF Offset and VF Stride may
>> @@ -426,6 +427,67 @@ const struct attribute_group sriov_dev_attr_group = {
>> .is_visible = sriov_attrs_are_visible,
>> };
>>
>> +#ifdef CONFIG_PCI_MSI
>> +static ssize_t vf_msix_vec_show(struct device *dev,
>> + struct device_attribute *attr, char *buf)
>> +{
>> + struct pci_dev *pdev = to_pci_dev(dev);
>> + int numb = pci_msix_vec_count(pdev);
>> + struct pci_dev *pfdev;
>> +
>> + if (numb < 0)
>> + return numb;
>> +
>> + pfdev = pci_physfn(pdev);
>> + if (!pfdev->driver || !pfdev->driver->sriov_set_msix_vec_count)
>> + return -EOPNOTSUPP;
>> +
> This doesn't make sense to me. You are getting the vector count for
> the PCI device and reporting that. Are you expecting to call this on
> the PF or the VFs? It seems like this should be a PF attribute and not
> be called on the individual VFs.
>
> If you are calling this on the VFs then it doesn't really make any
> sense anyway since the VF is not a "VF PCI dev representor" and
> shouldn't be treated as such. In my opinion if we are going to be
> doing per-port resource limiting that is something that might make
> more sense as a part of the devlink configuration for the VF since the
> actual change won't be visible to an assigned device.
if the op were just limited to nic ports, devlink may be used; but I believe Leon is trying to handle it from an sriov/vf perspective for other non-nic devices as well,
e.g., ib ports, nvme vf's (which don't have a port concept at all).
>> + return sprintf(buf, "%d\n", numb);
>> +}
>> +
>> +static ssize_t vf_msix_vec_store(struct device *dev,
>> + struct device_attribute *attr, const char *buf,
>> + size_t count)
>> +{
>> + struct pci_dev *vf_dev = to_pci_dev(dev);
>> + int val, ret;
>> +
>> + ret = kstrtoint(buf, 0, &val);
>> + if (ret)
>> + return ret;
>> +
>> + ret = pci_set_msix_vec_count(vf_dev, val);
>> + if (ret)
>> + return ret;
>> +
>> + return count;
>> +}
>> +static DEVICE_ATTR_RW(vf_msix_vec);
>> +#endif
>> +
>> +static struct attribute *sriov_vf_dev_attrs[] = {
>> +#ifdef CONFIG_PCI_MSI
>> + &dev_attr_vf_msix_vec.attr,
>> +#endif
>> + NULL,
>> +};
>> +
>> +static umode_t sriov_vf_attrs_are_visible(struct kobject *kobj,
>> + struct attribute *a, int n)
>> +{
>> + struct device *dev = kobj_to_dev(kobj);
>> +
>> + if (dev_is_pf(dev))
>> + return 0;
>> +
>> + return a->mode;
>> +}
>> +
>> +const struct attribute_group sriov_vf_dev_attr_group = {
>> + .attrs = sriov_vf_dev_attrs,
>> + .is_visible = sriov_vf_attrs_are_visible,
>> +};
>> +
>> int __weak pcibios_sriov_enable(struct pci_dev *pdev, u16 num_vfs)
>> {
>> return 0;
>> diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
>> index 3162f88fe940..20705ca94666 100644
>> --- a/drivers/pci/msi.c
>> +++ b/drivers/pci/msi.c
>> @@ -991,6 +991,35 @@ int pci_msix_vec_count(struct pci_dev *dev)
>> }
>> EXPORT_SYMBOL(pci_msix_vec_count);
>>
>> +/**
>> + * pci_set_msix_vec_count - change the reported number of MSI-X vectors
>> + * This function is applicable for SR-IOV VF because such devices allocate
>> + * their MSI-X table before they will run on the VMs and HW can't guess the
>> + * right number of vectors, so the HW allocates them statically and equally.
>> + * @dev: VF device that is going to be changed
>> + * @numb: amount of MSI-X vectors
>> + **/
>> +int pci_set_msix_vec_count(struct pci_dev *dev, int numb)
>> +{
>> + struct pci_dev *pdev = pci_physfn(dev);
>> +
>> + if (!dev->msix_cap || !pdev->msix_cap)
>> + return -EINVAL;
>> +
>> + if (dev->driver || !pdev->driver ||
>> + !pdev->driver->sriov_set_msix_vec_count)
>> + return -EOPNOTSUPP;
>> +
>> + if (numb < 0)
>> + /*
>> + * We don't support negative numbers for now,
>> + * but maybe in the future it will make sense.
>> + */
>> + return -EINVAL;
>> +
>> + return pdev->driver->sriov_set_msix_vec_count(dev, numb);
>> +}
>> +
> If you are going to have a set operation for this it would make sense
> to have a get operation. Your show operation seems unbalanced since
> you are expecting to call it on the VF directly which just seems
> wrong.
>
>> static int __pci_enable_msix(struct pci_dev *dev, struct msix_entry *entries,
>> int nvec, struct irq_affinity *affd, int flags)
>> {
>> diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
>> index fb072f4b3176..0af2222643c2 100644
>> --- a/drivers/pci/pci-sysfs.c
>> +++ b/drivers/pci/pci-sysfs.c
>> @@ -1557,6 +1557,7 @@ static const struct attribute_group *pci_dev_attr_groups[] = {
>> &pci_dev_hp_attr_group,
>> #ifdef CONFIG_PCI_IOV
>> &sriov_dev_attr_group,
>> + &sriov_vf_dev_attr_group,
>> #endif
>> &pci_bridge_attr_group,
>> &pcie_dev_attr_group,
>> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
>> index 5c59365092fa..1fd273077637 100644
>> --- a/drivers/pci/pci.h
>> +++ b/drivers/pci/pci.h
>> @@ -183,6 +183,7 @@ extern unsigned int pci_pm_d3hot_delay;
>>
>> #ifdef CONFIG_PCI_MSI
>> void pci_no_msi(void);
>> +int pci_set_msix_vec_count(struct pci_dev *dev, int numb);
>> #else
>> static inline void pci_no_msi(void) { }
>> #endif
>> @@ -502,6 +503,7 @@ resource_size_t pci_sriov_resource_alignment(struct pci_dev *dev, int resno);
>> void pci_restore_iov_state(struct pci_dev *dev);
>> int pci_iov_bus_range(struct pci_bus *bus);
>> extern const struct attribute_group sriov_dev_attr_group;
>> +extern const struct attribute_group sriov_vf_dev_attr_group;
>> #else
>> static inline int pci_iov_init(struct pci_dev *dev)
>> {
>> diff --git a/include/linux/pci.h b/include/linux/pci.h
>> index b32126d26997..a17cfc28eb66 100644
>> --- a/include/linux/pci.h
>> +++ b/include/linux/pci.h
>> @@ -856,6 +856,8 @@ struct module;
>> * e.g. drivers/net/e100.c.
>> * @sriov_configure: Optional driver callback to allow configuration of
>> * number of VFs to enable via sysfs "sriov_numvfs" file.
>> + * @sriov_set_msix_vec_count: Driver callback to change number of MSI-X vectors
>> + * exposed by the sysfs "vf_msix_vec" entry.
> Hopefully it is doing more than just changing the displayed sysfs
> value. What is the effect of changing that value on the actual system
> state? I'm assuming this is some limit that is enforced by the PF or
> the device firmware?
>
>
>> * @err_handler: See Documentation/PCI/pci-error-recovery.rst
>> * @groups: Sysfs attribute groups.
>> * @driver: Driver model structure.
>> @@ -871,6 +873,7 @@ struct pci_driver {
>> int (*resume)(struct pci_dev *dev); /* Device woken up */
>> void (*shutdown)(struct pci_dev *dev);
>> int (*sriov_configure)(struct pci_dev *dev, int num_vfs); /* On PF */
>> + int (*sriov_set_msix_vec_count)(struct pci_dev *vf, int msix_vec_count); /* On PF */
>> const struct pci_error_handlers *err_handler;
>> const struct attribute_group **groups;
>> struct device_driver driver;
>> @@ -2057,7 +2060,6 @@ void __iomem *pci_ioremap_wc_bar(struct pci_dev *pdev, int bar);
>>
>> #ifdef CONFIG_PCI_IOV
>> int pci_iov_virtfn_bus(struct pci_dev *dev, int id);
>> -int pci_iov_virtfn_devfn(struct pci_dev *dev, int id);
>>
>> int pci_enable_sriov(struct pci_dev *dev, int nr_virtfn);
>> void pci_disable_sriov(struct pci_dev *dev);
>> @@ -2402,6 +2404,10 @@ static inline bool pci_is_thunderbolt_attached(struct pci_dev *pdev)
>> void pci_uevent_ers(struct pci_dev *pdev, enum pci_ers_result err_type);
>> #endif
>>
>> +#ifdef CONFIG_PCI_IOV
>> +int pci_iov_virtfn_devfn(struct pci_dev *dev, int vf_id);
>> +#endif
>> +
>> /* Provide the legacy pci_dma_* API */
>> #include <linux/pci-dma-compat.h>
>>
>> --
>> 2.29.2
>>
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