Re: [libvirt] [PATCH v4 2/5] numa: describe siblings distances within cells
On 09/08/2017 08:47 AM, Wim Ten Have wrote:
From: Wim ten Have <wim.ten.have(a)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.
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>
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...
I didn't look closely at the patch since I'd like to understand how multi-cpu
cells are handled before doing so.
Regards,
Jim