Re: [PATCH 1/4] PCI: introduce VFs reference counter and simplify pci_vfs_assigned() implementation

[ethan zhao <ethan.zhao@oracle.com>]

On 2014/7/11 10:33, Alex Williamson wrote:
> On Fri, 2014-07-11 at 10:29 +0800, ethan zhao wrote:
>> On 2014/7/11 10:22, Alex Williamson wrote:
>>> On Fri, 2014-07-11 at 10:10 +0800, ethan zhao wrote:
>>>> Alex,
>>>>       Thanks for your reviewing, when I create the patch order, I thought
>>>> about the question you concerned for
>>>> quit a while, make every patch be independent to each other as possible
>>>> as I could, so we can do bisect when hit
>>>> problem.
>>>>
>>>>       I manage to take more time to figure out better patch order.
>>>>
>>>>       Thanks,
>>>>       Ethan
>>>>
>>>> On 2014/7/11 9:48, Alex Williamson wrote:
>>>>> Since there's no 0th patch, I guess I'll comment here.  This series is
>>>>> not bisectable, patch 1 breaks the existing implementation.  I'd
>>>>> suggest:
>>>>>
>>>>> patch 1 - fix i40e
>>>>                i40e only could be fixed with new interface, so it couldn't
>>>> be the first one.
>>> It looks like i40e just has it's own copy of pci_vfs_assigned(), why
>>> can't your current patch 4/4 be applied now?
>>    Yes, i40e has its local copy of pci_vfs_assigned(),it could be
>> simplified .
>> with new interface,in another word, its a user of new interface.
> It's a user of the existing interface.  You're missing the point,
> abstract all the users of the assigned dev_flags first, then you're free
> to fix the implementation of the interface in one shot without breaking
> anything.
  Great,you hit the center this time, agree !
>>>>> patch 2 - create assign/deassign that uses dev_flags
>>>>                This will be the first ?
>>>>> patch 3 - convert users to new interface
>>>>                Have to be the later step.
>>>>> patch 4 - convert interface to use atomic_t
>>>>                Could it be standalone step ?
>>>>
>>>>     Let me think about it.
>>>>
>>>>> IMHO, the assigned flag is a horrible hack and I don't know why drivers
>>>>> like xenback need to use it.  KVM needs to use it because it doesn't
>>>>> actually have a driver to bind to when a device is assigned, it's happy
>>>>> to assign devices without any driver.  Thanks,
>>>>>
>>>>> Alex
>>>>>
>>>>>
>>>>> On Fri, 2014-07-11 at 08:47 +0800, Ethan Zhao wrote:
>>>>>> Current implementation of helper function pci_vfs_assigned() is a little complex, to
>>>>>> get sum of VFs that assigned to VM, access low level configuration space register and
>>>>>> then loop in traversing device tree.
>>>>>>
>>>>>> This patch introduce an atomic reference counter for VFs that assigned to VM in struct
>>>>>> pci_sriov, and compose two more helper functions
>>>>>>
>>>>>> pci_sriov_assign_device(),
>>>>>> pci_sriov_deassign_device()
>>>>>>
>>>>>> to replace manipulation to device flag and the meanwhile increase and decease the counter.
>>>>>>
>>>>>> Passed building on 3.15.5
>>>>>>
>>>>>> Signed-off-by: Ethan Zhao <ethan.zhao@oracle.com>
>>>>>> ---
>>>>>>     drivers/pci/iov.c   |   65 ++++++++++++++++++++++++++++----------------------
>>>>>>     drivers/pci/pci.h   |    1 +
>>>>>>     include/linux/pci.h |    4 +++
>>>>>>     3 files changed, 41 insertions(+), 29 deletions(-)
>>>>>>
>>>>>> diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
>>>>>> index de7a747..72e267f 100644
>>>>>> --- a/drivers/pci/iov.c
>>>>>> +++ b/drivers/pci/iov.c
>>>>>> @@ -382,6 +382,7 @@ found:
>>>>>>     	iov->nres = nres;
>>>>>>     	iov->ctrl = ctrl;
>>>>>>     	iov->total_VFs = total;
>>>>>> +	atomic_set(&iov->VFs_assigned_cnt, 0);
>>>>>>     	iov->offset = offset;
>>>>>>     	iov->stride = stride;
>>>>>>     	iov->pgsz = pgsz;
>>>>>> @@ -603,45 +604,51 @@ int pci_num_vf(struct pci_dev *dev)
>>>>>>     EXPORT_SYMBOL_GPL(pci_num_vf);
>>>>>>     
>>>>>>     /**
>>>>>> - * pci_vfs_assigned - returns number of VFs are assigned to a guest
>>>>>> - * @dev: the PCI device
>>>>>> + * pci_vfs_assigned - returns number of VFs are assigned to VM
>>>>>> + * @dev: the physical PCI device that contains the VFs.
>>>>>>      *
>>>>>> - * Returns number of VFs belonging to this device that are assigned to a guest.
>>>>>> + * Returns number of VFs belonging to this device that are assigned to VM.
>>>>>>      * If device is not a physical function returns 0.
>>>>>>      */
>>>>>>     int pci_vfs_assigned(struct pci_dev *dev)
>>>>>>     {
>>>>>> -	struct pci_dev *vfdev;
>>>>>> -	unsigned int vfs_assigned = 0;
>>>>>> -	unsigned short dev_id;
>>>>>> -
>>>>>> -	/* only search if we are a PF */
>>>>>>     	if (!dev->is_physfn)
>>>>>>     		return 0;
>>>>>> +	if (dev->sriov)
>>>>>> +		return atomic_read(&dev->sriov->VFs_assigned_cnt);
>>>>>> +	return 0;
>>>>>> +}
>>>>>> +EXPORT_SYMBOL_GPL(pci_vfs_assigned);
>>>>>>     
>>>>>> -	/*
>>>>>> -	 * determine the device ID for the VFs, the vendor ID will be the
>>>>>> -	 * same as the PF so there is no need to check for that one
>>>>>> -	 */
>>>>>> -	pci_read_config_word(dev, dev->sriov->pos + PCI_SRIOV_VF_DID, &dev_id);
>>>>>> -
>>>>>> -	/* loop through all the VFs to see if we own any that are assigned */
>>>>>> -	vfdev = pci_get_device(dev->vendor, dev_id, NULL);
>>>>>> -	while (vfdev) {
>>>>>> -		/*
>>>>>> -		 * It is considered assigned if it is a virtual function with
>>>>>> -		 * our dev as the physical function and the assigned bit is set
>>>>>> -		 */
>>>>>> -		if (vfdev->is_virtfn && (vfdev->physfn == dev) &&
>>>>>> -		    (vfdev->dev_flags & PCI_DEV_FLAGS_ASSIGNED))
>>>>>> -			vfs_assigned++;
>>>>>> -
>>>>>> -		vfdev = pci_get_device(dev->vendor, dev_id, vfdev);
>>>>>> -	}
>>>>>> +/**
>>>>>> + * pci_sriov_assign_device - assign device to VM
>>>>>> + * @pdev: the device to be assigned.
>>>>>> + */
>>>>>> +void pci_sriov_assign_device(struct pci_dev *pdev)
>>>>>> +{
>>>>>> +	pdev->dev_flags |= PCI_DEV_FLAGS_ASSIGNED;
>>>>>> +	if (pdev->is_virtfn && !pdev->is_physfn)
>>>>>> +		if (pdev->physfn)
>>>>>> +			if (pdev->physfn->sriov)
>>>>>> +				atomic_inc(&pdev->physfn->sriov->
>>>>>> +						VFs_assigned_cnt);
>>>>>> +}
>>>>>> +EXPORT_SYMBOL_GPL(pci_sriov_assign_device);
>>>>>>     
>>>>>> -	return vfs_assigned;
>>>>>> +/**
>>>>>> + * pci_sriov_deassign_device - deasign device from VM
>>>>>> + * @pdev: the device to be deassigned.
>>>>>> + */
>>>>>> +void pci_sriov_deassign_device(struct pci_dev *pdev)
>>>>>> +{
>>>>>> +	pdev->dev_flags &= ~PCI_DEV_FLAGS_ASSIGNED;
>>>>>> +	if (pdev->is_virtfn && !pdev->is_physfn)
>>>>>> +		if (pdev->physfn)
>>>>>> +			if (pdev->physfn->sriov)
>>>>>> +				atomic_dec(&pdev->physfn->sriov->
>>>>>> +						VFs_assigned_cnt);
>>>>>>     }
>>>>>> -EXPORT_SYMBOL_GPL(pci_vfs_assigned);
>>>>>> +EXPORT_SYMBOL_GPL(pci_sriov_deassign_device);
>>>>>>     
>>>>>>     /**
>>>>>>      * pci_sriov_set_totalvfs -- reduce the TotalVFs available
>>>>>> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
>>>>>> index 6bd0822..d17bda2 100644
>>>>>> --- a/drivers/pci/pci.h
>>>>>> +++ b/drivers/pci/pci.h
>>>>>> @@ -235,6 +235,7 @@ struct pci_sriov {
>>>>>>     	u32 pgsz;		/* page size for BAR alignment */
>>>>>>     	u8 link;		/* Function Dependency Link */
>>>>>>     	u16 driver_max_VFs;	/* max num VFs driver supports */
>>>>>> +	atomic_t VFs_assigned_cnt; /* counter of VFs assigned to VM */
>>>>>>     	struct pci_dev *dev;	/* lowest numbered PF */
>>>>>>     	struct pci_dev *self;	/* this PF */
>>>>>>     	struct mutex lock;	/* lock for VF bus */
>>>>>> diff --git a/include/linux/pci.h b/include/linux/pci.h
>>>>>> index aab57b4..5cf6833 100644
>>>>>> --- a/include/linux/pci.h
>>>>>> +++ b/include/linux/pci.h
>>>>>> @@ -1601,6 +1601,8 @@ int pci_enable_sriov(struct pci_dev *dev, int nr_virtfn);
>>>>>>     void pci_disable_sriov(struct pci_dev *dev);
>>>>>>     int pci_num_vf(struct pci_dev *dev);
>>>>>>     int pci_vfs_assigned(struct pci_dev *dev);
>>>>>> +void pci_sriov_assign_device(struct pci_dev *dev);
>>>>>> +void pci_sriov_deassign_device(struct pci_dev *dev);
>>>>>>     int pci_sriov_set_totalvfs(struct pci_dev *dev, u16 numvfs);
>>>>>>     int pci_sriov_get_totalvfs(struct pci_dev *dev);
>>>>>>     #else
>>>>>> @@ -1610,6 +1612,8 @@ static inline void pci_disable_sriov(struct pci_dev *dev) { }
>>>>>>     static inline int pci_num_vf(struct pci_dev *dev) { return 0; }
>>>>>>     static inline int pci_vfs_assigned(struct pci_dev *dev)
>>>>>>     { return 0; }
>>>>>> +static inline void pci_sriov_assign_device(struct pci_dev *dev) { }
>>>>>> +static inline void pci_sriov_deassign_device(struct pci_dev *dev) { }
>>>>>>     static inline int pci_sriov_set_totalvfs(struct pci_dev *dev, u16 numvfs)
>>>>>>     { return 0; }
>>>>>>     static inline int pci_sriov_get_totalvfs(struct pci_dev *dev)
>>>
>
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