Re: [PATCH v2 1/8] powerpc/xive: Use cpu_to_node() instead of ibm,chip-id property

[Daniel Henrique Barboza <danielhb@linux.ibm.com>]

On 3/12/21 6:53 AM, Cédric Le Goater wrote:
> On 3/12/21 2:55 AM, David Gibson wrote:
>> On Tue, 9 Mar 2021 18:26:35 +0100
>> Cédric Le Goater <clg@kaod.org> wrote:
>>
>>> On 3/9/21 6:08 PM, Daniel Henrique Barboza wrote:
>>>>
>>>>
>>>> On 3/9/21 12:33 PM, Cédric Le Goater wrote:
>>>>> On 3/8/21 6:13 PM, Greg Kurz wrote:
>>>>>> On Wed, 3 Mar 2021 18:48:50 +0100
>>>>>> Cédric Le Goater <clg@kaod.org> wrote:
>>>>>>   
>>>>>>> The 'chip_id' field of the XIVE CPU structure is used to choose a
>>>>>>> target for a source located on the same chip when possible. This field
>>>>>>> is assigned on the PowerNV platform using the "ibm,chip-id" property
>>>>>>> on pSeries under KVM when NUMA nodes are defined but it is undefined
>>>>>>
>>>>>> This sentence seems to have a syntax problem... like it is missing an
>>>>>> 'and' before 'on pSeries'.
>>>>>
>>>>> ah yes, or simply a comma.
>>>>>   
>>>>>>> under PowerVM. The XIVE source structure has a similar field
>>>>>>> 'src_chip' which is only assigned on the PowerNV platform.
>>>>>>>
>>>>>>> cpu_to_node() returns a compatible value on all platforms, 0 being the
>>>>>>> default node. It will also give us the opportunity to set the affinity
>>>>>>> of a source on pSeries when we can localize them.
>>>>>>>   
>>>>>>
>>>>>> IIUC this relies on the fact that the NUMA node id is == to chip id
>>>>>> on PowerNV, i.e. xc->chip_id which is passed to OPAL remain stable
>>>>>> with this change.
>>>>>
>>>>> Linux sets the NUMA node in numa_setup_cpu(). On pseries, the hcall
>>>>> H_HOME_NODE_ASSOCIATIVITY returns the node id if I am correct (Daniel
>>>>> in Cc:)
>>>   [...]
>>>>>
>>>>> On PowerNV, Linux uses "ibm,associativity" property of the CPU to find
>>>>> the node id. This value is built from the chip id in OPAL, so the
>>>>> value returned by cpu_to_node(cpu) and the value of the "ibm,chip-id"
>>>>> property are unlikely to be different.
>>>>>
>>>>> cpu_to_node(cpu) is used in many places to allocate the structures
>>>>> locally to the owning node. XIVE is not an exception (see below in the
>>>>> same patch), it is better to be consistent and get the same information
>>>>> (node id) using the same routine.
>>>>>
>>>>>
>>>>> In Linux, "ibm,chip-id" is only used in low level PowerNV drivers :
>>>>> LPC, XSCOM, RNG, VAS, NX. XIVE should be in that list also but skiboot
>>>>> unifies the controllers of the system to only expose one the OS. This
>>>>> is problematic and should be changed but it's another topic.
>>>>>
>>>>>   
>>>>>> On the other hand, you have the pSeries case under PowerVM that
>>>>>> doesn't xc->chip_id, which isn't passed to any hcall AFAICT.
>>>>>
>>>>> yes "ibm,chip-id" is an OPAL concept unfortunately and it has no meaning
>>>>> under PAPR. xc->chip_id on pseries (PowerVM) will contains an invalid
>>>>> chip id.
>>>>>
>>>>> QEMU/KVM exposes "ibm,chip-id" but it's not used. (its value is not
>>>>> always correct btw)
>>>>
>>>>
>>>> If you have a way to reliably reproduce this, let me know and I'll fix it
>>>> up in QEMU.
>>>
>>> with :
>>>
>>>     -smp 4,cores=1,maxcpus=8 -object memory-backend-ram,id=ram-node0,size=2G -numa node,nodeid=0,cpus=0-1,cpus=4-5,memdev=ram-node0 -object memory-backend-ram,id=ram-node1,size=2G -numa node,nodeid=1,cpus=2-3,cpus=6-7,memdev=ram-node1
>>>
>>> # dmesg | grep numa
>>> [    0.013106] numa: Node 0 CPUs: 0-1
>>> [    0.013136] numa: Node 1 CPUs: 2-3
>>>
>>> # dtc -I fs /proc/device-tree/cpus/ -f | grep ibm,chip-id
>>> 		ibm,chip-id = <0x01>;
>>> 		ibm,chip-id = <0x02>;
>>> 		ibm,chip-id = <0x00>;
>>> 		ibm,chip-id = <0x03>;
>>>
>>> with :
>>>
>>>    -smp 4,cores=4,maxcpus=8,threads=1 -object memory-backend-ram,id=ram-node0,size=2G -numa node,nodeid=0,cpus=0-1,cpus=4-5,memdev=ram-node0 -object memory-backend-ram,id=ram-node1,size=2G -numa node,nodeid=1,cpus=2-3,cpus=6-7,memdev=ram-node1
>>>
>>> # dmesg | grep numa
>>> [    0.013106] numa: Node 0 CPUs: 0-1
>>> [    0.013136] numa: Node 1 CPUs: 2-3
>>>
>>> # dtc -I fs /proc/device-tree/cpus/ -f | grep ibm,chip-id
>>> 		ibm,chip-id = <0x00>;
>>> 		ibm,chip-id = <0x00>;
>>> 		ibm,chip-id = <0x00>;
>>> 		ibm,chip-id = <0x00>;
>>>
>>> I think we should simply remove "ibm,chip-id" since it's not used and
>>> not in the PAPR spec.
>>
>> As I mentioned to Daniel on our call this morning, oddly it *does*
>> appear to be used in the RHEL kernel, even though that's 4.18 based.
>> This patch seems to have caused a minor regression; not in the
>> identification of NUMA nodes, but in the number of sockets shown be
>> lscpu, etc.  See https://bugzilla.redhat.com/show_bug.cgi?id=1934421
>> for more information.
> 
> Yes. The property "ibm,chip-id" is wrongly calculated in QEMU. If we
> remove it, we get with 4.18.0-295.el8.ppc64le or 5.12.0-rc2 :
> 
>     [root@localhost ~]# lscpu
>     Architecture:        ppc64le
>     Byte Order:          Little Endian
>     CPU(s):              128
>     On-line CPU(s) list: 0-127
>     Thread(s) per core:  4
>     Core(s) per socket:  16
>     Socket(s):           2
>     NUMA node(s):        2
>     Model:               2.2 (pvr 004e 1202)
>     Model name:          POWER9 (architected), altivec supported
>     Hypervisor vendor:   KVM
>     Virtualization type: para
>     L1d cache:           32K
>     L1i cache:           32K
>     NUMA node0 CPU(s):   0-63
>     NUMA node1 CPU(s):   64-127
> 
>     [root@localhost ~]# grep . /sys/devices/system/cpu/*/topology/physical_package_id
>     /sys/devices/system/cpu/cpu0/topology/physical_package_id:-1
>     /sys/devices/system/cpu/cpu100/topology/physical_package_id:-1
>     /sys/devices/system/cpu/cpu101/topology/physical_package_id:-1
>     /sys/devices/system/cpu/cpu102/topology/physical_package_id:-1
>     /sys/devices/system/cpu/cpu103/topology/physical_package_id:-1
>     ....
> 
> "ibm,chip-id" is still being used on some occasion on pSeries machines.
> This is wrong :/ The problem is :
> 
>    #define topology_physical_package_id(cpu)      (cpu_to_chip_id(cpu))
> 
> We should be using cpu_to_node().


IIUC the "real fix" then is this change you mentioned above, together with
this xive patch as well, to stop using ibm,chip-id for good in the pserie
  kernel. With these changes QEMU can remove 'ibm,chip-id' from the pseries
machine without impact. Is this correct?

If that's the case, then I believe it's ok to go forward with the QEMU side
change (just for 6.0.0 and newer machines). Or should I wait for the kernel
changes to be merged upstream first?


Thanks,


DHB


> 
> C.
> 
>>
>> Since the value was used by some PAPR kernels - even if they shouldn't
>> have - I think we should only remove this for newer machine types.  We
>> also need to check what we're not supplying that the guest kernel is
>> showing a different number of sockets than specified on the qemu
>> command line.
>>
>>>
>>> Thanks,
>>>
>>> C.
>>>
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>>
>>
>