Re: [PATCH] pci, add sysfs numa_node write function

[Prarit Bhargava <prarit@redhat.com>]

On 10/15/2014 03:47 PM, Prarit Bhargava wrote:
> On 10/15/2014 03:23 PM, Bjorn Helgaas wrote:
>> Hi Prarit,
>>
>> On Wed, Oct 15, 2014 at 1:05 PM, Prarit Bhargava <prarit@redhat.com> wrote:
>>> Consider a multi-node, multiple pci root bridge system which can be
>>> configured into one large node or one node/socket.  When configuring the
>>> system the numa_node value for each PCI root bridge is always set
>>> incorrectly to -1, or NUMA_NO_NODE, rather than to the node value of each
>>> socket.  Each PCI device inherits the numa value directly from it's parent
>>> device, so that the NUMA_NO_NODE value is passed through the entire PCI
>>> tree.
>>>
>>> Some new drivers, such as the Intel QAT driver, drivers/crypto/qat,
>>> require that a specific node be assigned to the device in order to
>>> achieve maximum performance for the device, and will fail to load if the
>>> device has NUMA_NO_NODE.
>>
>> It seems ... unfriendly for a driver to fail to load just because it
>> can't guarantee maximum performance.  Out of curiosity, where does
>> this actually happen?  I had a quick look for NUMA_NO_NODE and
>> module_init() functions in drivers/crypto/qat, and I didn't see the
>> spot.
> 
> The whole point of the Intel QAT driver is to guarantee max performance.  If
> that is not possible the driver should not load (according to the thread
> mentioned below)
> 

Whups.  This thread:

http://marc.info/?l=linux-crypto-vger&m=141279031626999&w=2


>>
>>> The driver would load if the numa_node value
>>> was equal to or greater than -1 and quickly hacking the driver results in
>>> a functional QAT driver.
>>>
>>> Using lspci and numactl it is easy to determine what the numa value should
>>> be.  The problem is that there is no way to set it.  This patch adds a
>>> store function for the PCI device's numa_node value.
>>
>> I'm not familiar with numactl.  It sounds like it can show you the
>> NUMA topology?  Where does that information come from?
> 
> You can map at least what nodes are available (although I suppose you can get
> the same information from dmesg).  You have to do a bit of hunting through the
> PCI tree to determine the root PCI devices, but you can determine which root
> device is connected to which node.
> 
>>
>>> To use this, one can do
>>>
>>> echo 3 > /sys/devices/pci0000:ff/0000:ff:1f.3/numa_node
>>>
>>> to set the numa node for PCI device 0000:ff:1f.3.
>>
>> It definitely seems wrong that we don't set the node number correctly.
>> pci_acpi_scan_root() sets the node number by looking for a _PXM method
>> that applies to the host bridge.  Why does that not work in this case?
>>  Does the BIOS not supply _PXM?
> 
> Yeah ... unfortunately the BIOS is broken in this case.  And I know what you're
> thinking ;) -- why not get the BIOS fixed?  I'm through relying on BIOS fixes
> which can take six months to a year to appear in a production version... I've
> been bitten too many times by promises of BIOS fixes that never materialize.
> 
> We have systems that only have a support cycle of 3 years, and things like ACPI
> _PXM updates are at the bottom of the list :/.
> 
> FWIW, on this particular system I have a filed a bug with the vendor.
> 
>>
>> If there's information that numactl uses, maybe the kernel should use that, too?
>>
>> A sysfs interface might be a useful workaround, but obviously it would
>> be far better if we could fix the BIOS and/or kernel so the workaround
>> isn't necessary in the first place.
> 
> Yep ... but like I said, I don't think anyone wants to wait a year.  What if we
> never see a fix?
> 
> Side issue:  While investigating this I noticed that plain kmalloc() is used in
> the setup code.  Is there a reason we don't use kmalloc_node() in
> pci_alloc_dev(), and other allocation functions?  It seems like we should be to
> optimize system performance.  OTOH ... I haven't done any measurements to see if
> it actually makes a difference :)
> 
> P.
> 
>>
>> Bjorn
>>
>>> Cc: Myron Stowe <mstowe@redhat.com>
>>> Cc: Bjorn Helgaas <bhelgaas@google.com>
>>> Cc: linux-pci@vger.kernel.org
>>> Signed-off-by: Prarit Bhargava <prarit@redhat.com>
>>> ---
>>>  drivers/pci/pci-sysfs.c |   23 ++++++++++++++++++++++-
>>>  1 file changed, 22 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
>>> index 92b6d9a..c05ed30 100644
>>> --- a/drivers/pci/pci-sysfs.c
>>> +++ b/drivers/pci/pci-sysfs.c
>>> @@ -221,12 +221,33 @@ static ssize_t enabled_show(struct device *dev, struct device_attribute *attr,
>>>  static DEVICE_ATTR_RW(enabled);
>>>
>>>  #ifdef CONFIG_NUMA
>>> +static ssize_t numa_node_store(struct device *dev,
>>> +                              struct device_attribute *attr,
>>> +                              const char *buf, size_t count)
>>> +{
>>> +       int node, ret;
>>> +
>>> +       if (!capable(CAP_SYS_ADMIN))
>>> +               return -EPERM;
>>> +
>>> +       ret = kstrtoint(buf, 0, &node);
>>> +       if (ret)
>>> +               return ret;
>>> +
>>> +       if (!node_online(node))
>>> +               return -EINVAL;
>>> +
>>> +       dev->numa_node = node;
>>> +
>>> +       return count;
>>> +}
>>> +
>>>  static ssize_t numa_node_show(struct device *dev, struct device_attribute *attr,
>>>                               char *buf)
>>>  {
>>>         return sprintf(buf, "%d\n", dev->numa_node);
>>>  }
>>> -static DEVICE_ATTR_RO(numa_node);
>>> +static DEVICE_ATTR_RW(numa_node);
>>>  #endif
>>>
>>>  static ssize_t dma_mask_bits_show(struct device *dev,
>>> --
>>> 1.7.9.3
>>>
>>
>>
>