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

From: ethan zhao <[email-masked]>
Date: Fri, 11 Jul 2014 10:29:12 +0800

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.

  Thanks,
  Ethan
>
>>> 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 <[email-masked]>
>>>> ---
>>>>    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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