[libvirt] [PATCH v4 2/5] numa: describe siblings distances within cells
Wim ten Have
wim.ten.have at oracle.com
Thu Oct 12 10:37:54 UTC 2017
On Fri, 6 Oct 2017 08:49:46 -0600
Jim Fehlig <jfehlig at suse.com> wrote:
> On 09/08/2017 08:47 AM, Wim Ten Have wrote:
> > From: Wim ten Have <wim.ten.have at oracle.com>
> >
> > Add libvirtd NUMA cell domain administration functionality to
> > describe underlying cell id sibling distances in full fashion
> > when configuring HVM guests.
>
> May I suggest wording this paragraph as:
>
> Add support for describing sibling vCPU distances within a domain's vNUMA cell
> configuration.
See below (v5 comment).
> > Schema updates are made to docs/schemas/cputypes.rng enforcing domain
> > administration to follow the syntax below the numa cell id and
> > docs/schemas/basictypes.rng to add "numaDistanceValue".
>
> I'm not sure this paragraph is needed in the commit message.
>
> > A minimum value of 10 representing the LOCAL_DISTANCE as 0-9 are
> > reserved values and can not be used as System Locality Distance Information.
> > A value of 20 represents the default setting of REMOTE_DISTANCE
> > where a maximum value of 255 represents UNREACHABLE.
> >
> > Effectively any cell sibling can be assigned a distance value where
> > practically 'LOCAL_DISTANCE <= value <= UNREACHABLE'.
> >
> > [below is an example of a 4 node setup]
> >
> > <cpu>
> > <numa>
> > <cell id='0' cpus='0' memory='2097152' unit='KiB'>
> > <distances>
> > <sibling id='0' value='10'/>
> > <sibling id='1' value='21'/>
> > <sibling id='2' value='31'/>
> > <sibling id='3' value='41'/>
> > </distances>
> > </cell>
> > <cell id='1' cpus='1' memory='2097152' unit='KiB'>
> > <distances>
> > <sibling id='0' value='21'/>
> > <sibling id='1' value='10'/>
> > <sibling id='2' value='31'/>
> > <sibling id='3' value='41'/>
> > </distances>
> > </cell>
> > <cell id='2' cpus='2' memory='2097152' unit='KiB'>
> > <distances>
> > <sibling id='0' value='31'/>
> > <sibling id='1' value='21'/>
> > <sibling id='2' value='10'/>
> > <sibling id='3' value='21'/>
> > </distances>
> > <cell id='3' cpus='3' memory='2097152' unit='KiB'>
> > <distances>
> > <sibling id='0' value='41'/>
> > <sibling id='1' value='31'/>
> > <sibling id='2' value='21'/>
> > <sibling id='3' value='10'/>
> > </distances>
> > </cell>
> > </numa>
> > </cpu>
>
> How would this look when having more than one cpu in a cell? I suppose something
> like
>
> <cpu>
> <numa>
> <cell id='0' cpus='0-3' memory='2097152' unit='KiB'>
> <distances>
> <sibling id='0' value='10'/>
> <sibling id='1' value='10'/>
> <sibling id='2' value='10'/>
> <sibling id='3' value='10'/>
> <sibling id='4' value='21'/>
> <sibling id='5' value='21'/>
> <sibling id='6' value='21'/>
> <sibling id='7' value='21'/>
> </distances>
> </cell>
> <cell id='1' cpus='4-7' memory='2097152' unit='KiB'>
> <distances>
> <sibling id='0' value='21'/>
> <sibling id='1' value='21'/>
> <sibling id='2' value='21'/>
> <sibling id='3' value='21'/>
> <sibling id='4' value='10'/>
> <sibling id='5' value='10'/>
> <sibling id='6' value='10'/>
> <sibling id='7' value='10'/>
> </distances>
> </cell>
> </numa>
> </cpu>
Nope. That machine seems to make a 2 node vNUMA setup.
Where;
* NUMA node(0) defined by <cell id='0'> holds 4 (cores)
cpus '0-3' with 2GByte of dedicated memory.
* NUMA node(1) defined by <cell id='1'> holds 4 (cores)
cpus '4-7' with 2GByte of dedicated memory.
<cpu>
<numa>
<cell id='0' cpus='0-3' memory='2097152' unit='KiB'>
<distances>
<sibling id='0' value='10'/>
<sibling id='1' value='21'/>
</distances>
</cell>
<cell id='1' cpus='4-7' memory='2097152' unit='KiB'>
<distances>
<sibling id='0' value='21'/>
<sibling id='1' value='10'/>
</distances>
</cell>
</numa>
</cpu>
Specific configuration would typically report below when examined from
within the guest domain; (despite ignorance in this example that it
_DOES_ concern a single socket 8 cpu machine).
[root at f25 ~]# lscpu
Architecture: x86_64
CPU op-mode(s): 32-bit, 64-bit
Byte Order: Little Endian
CPU(s): 8
On-line CPU(s) list: 0-7
Thread(s) per core: 1
Core(s) per socket: 8
Socket(s): 1
*> NUMA node(s): 2
Vendor ID: AuthenticAMD
CPU family: 21
Model: 2
Model name: AMD FX-8320E Eight-Core Processor
Stepping: 0
CPU MHz: 3210.862
BogoMIPS: 6421.83
Virtualization: AMD-V
Hypervisor vendor: Xen
Virtualization type: full
L1d cache: 16K
L1i cache: 64K
L2 cache: 2048K
L3 cache: 8192K
*> NUMA node0 CPU(s): 0-3
*> NUMA node1 CPU(s): 4-7
Flags: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt pdpe1gb rdtscp lm rep_good nopl cpuid extd_apicid pni pclmulqdq ssse3 fma cx16 sse4_1 sse4_2 x2apic popcnt aes xsave avx f16c hypervisor lahf_lm svm cr8_legacy abm sse4a misalignsse 3dnowprefetch ibs xop lwp fma4 tbm vmmcall bmi1 arat npt lbrv nrip_save tsc_scale vmcb_clean decodeassists pausefilter
[root at f25 ~]# numactl -H
available: 2 nodes (0-1)
node 0 cpus: 0 1 2 3
node 0 size: 1990 MB
node 0 free: 1786 MB
node 1 cpus: 4 5 6 7
node 1 size: 1950 MB
node 1 free: 1820 MB
node distances:
node 0 1
0: 10 21
1: 21 10
> In the V3 thread you mentioned "And to reduce even more we could also
> remove LOCAL_DISTANCES as they make a constant factor where; (cell_id ==
> sibling_id)". In the above example cell_id 1 == sibling_id 1, but it is not
> LOCAL_DISTANCE.
>
> > Whenever a sibling id the cell LOCAL_DISTANCE does apply and for any
> > sibling id not being covered a default of REMOTE_DISTANCE is used
> > for internal computations.
>
> I'm having a hard time understanding this sentence...
Me.2
> I didn't look closely at the patch since I'd like to understand how multi-cpu
> cells are handled before doing so.
Let me prepare v5. I found a silly error in code being fixed and
given above commented confusion like to take a better approach under
the commit messages and witin the cover letter.
Regards,
- Wim.
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