Re: [libvirt] [V3] RFC for support cache tune in libvirt

<cache> <bank type="l3" size="56320" units="KiB" cpus="0,2,3,6,7,8"/> <bank type="l3" size="56320" units="KiB" cpus="3,4,5,9,10,11"/>

<bank type="l2" size="256" units="KiB" cpus="0"/>

<bank type="l2" size="256" units="KiB" cpus="2"/> <bank type="l2" size="256" units="KiB" cpus="3"/> <bank type="l2" size="256" units="KiB" cpus="4"/> <bank type="l2" size="256" units="KiB" cpus="5"/> <bank type="l2" size="256" units="KiB" cpus="6"/> <bank type="l2" size="256" units="KiB" cpus="7"/> <bank type="l2" size="256" units="KiB" cpus="8"/> <bank type="l2" size="256" units="KiB" cpus="9"/> <bank type="l2" size="256" units="KiB" cpus="10"/> <bank type="l2" size="256" units="KiB" cpus="11"/> <bank type="l1i" size="256" units="KiB" cpus="0"/> <bank type="l1i" size="256" units="KiB" cpus="1"/> <bank type="l1i" size="256" units="KiB" cpus="2"/> <bank type="l1i" size="256" units="KiB" cpus="3"/> <bank type="l1i" size="256" units="KiB" cpus="4"/> <bank type="l1i" size="256" units="KiB" cpus="5"/> <bank type="l1i" size="256" units="KiB" cpus="6"/> <bank type="l1i" size="256" units="KiB" cpus="7"/> <bank type="l1i" size="256" units="KiB" cpus="8"/> <bank type="l1i" size="256" units="KiB" cpus="9"/> <bank type="l1i" size="256" units="KiB" cpus="10"/> <bank type="l1i" size="256" units="KiB" cpus="11"/> <bank type="l1d" size="256" units="KiB" cpus="0"/> <bank type="l1d" size="256" units="KiB" cpus="1"/> <bank type="l1d" size="256" units="KiB" cpus="2"/> <bank type="l1d" size="256" units="KiB" cpus="3"/> <bank type="l1d" size="256" units="KiB" cpus="4"/> <bank type="l1d" size="256" units="KiB" cpus="5"/> <bank type="l1d" size="256" units="KiB" cpus="6"/> <bank type="l1d" size="256" units="KiB" cpus="7"/> <bank type="l1d" size="256" units="KiB" cpus="8"/> <bank type="l1d" size="256" units="KiB" cpus="9"/> <bank type="l1d" size="256" units="KiB" cpus="10"/> <bank type="l1d" size="256" units="KiB" cpus="11"/> </cache>

which shows each socket has its own dedicated L3 cache, and each core has its own L2 & L1 cache. > 2. Extend capabilities outputs. > > virsh capabilities | grep resctrl > <cpu> > ... > <resctrl name='L3' unit='KiB' cache_size='56320' cache_unit='2816'/> > </cpu> > > This will tell that the host have enabled resctrl(which you can find it in /sys/fs/resctrl), > And it supports to allocate 'L3' type cache, total 'L3' cache size is 56320 KiB, and the minimum unit size of 'L3' cache is 2816 KiB. > P.S. L3 cache size unit is the minum l3 cache unit can be allocated. It's hardware related and can not be changed. If we're already reported cache in the capabilities from step one, then it ought to be extendable to cover this reporting. <cache> <bank type="l3" size="56320" units="KiB" cpus="0,2,3,6,7,8"> <control unit="KiB" min="2816"/> </bank> <bank type="l3" size="56320" units="KiB" cpus="3,4,5,9,10,11"> <control unit="KiB" min="2816"/> </bank> </cache>

note how we report the control info for both l3 caches, since they come from separate sockets and thus could conceivably report different info if different CPUs were in each socket. > 3. Add new virsh command 'nodecachestats': > This API is to expose vary cache resouce left on each hardware (cpu socket). > > It will be formated as: > > <resource_type>.<resource_id>: left size KiB > > for example I have a 2 socket cpus host, and I'v enabled cat_l3 feature only > > root@s2600wt:~/linux# virsh nodecachestats > L3.0 : 56320 KiB > L3.1 : 56320 KiB > > P.S. resource_type can be L3, L3DATA, L3CODE, L2 for now. This feels like something we should have in the capabilities XML too rather than a new command <cache> <bank type="l3" size="56320" units="KiB" cpus="0,2,3,6,7,8"> <control unit="KiB" min="2816" avail="56320/> </bank> <bank type="l3" size="56320" units="KiB" cpus="3,4,5,9,10,11"> <control unit="KiB" min="2816" avail="56320"/> </bank> </cache> > 4. Add new interface to manage how many cache can be allociated for a domain > > root@s2600wt:~/linux# virsh cachetune kvm02 --l3.count 2 > > root@s2600wt:~/linux# virsh cachetune kvm02 > l3.count : 2 > > This will allocate 2 units(2816 * 2) l3 cache for domain kvm02 > > ## Domain XML changes > > Cache Tuneing > > <domain> > ... > <cachetune> > <l3_cache_count>2</l3_cache_count> > </cachetune> > ... > </domain> IIUC, the kernel lets us associate individual PIDs with each cache. Since each vCPU is a PID, this means we are able to allocate different cache size to different CPUs. So we need to be able to represent that in the XML. I think we should also represent the allocation in a normal size (ie KiB), not in count of min unit.

So eg this shows allocating two cache banks and giving one to the first 4 cpus, and one to the second 4 cpus <cachetune> <bank type="l3" size="5632" unit="KiB" cpus="0,1,2,3"/> <bank type="l3" size="5632" unit="KiB" cpus="4,5,6,7"/>

</cachetune> Regards, Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://entangle-photo.org -o- http://search.cpan.org/~danberr/ :|