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xen-devel
Re: [Xen-devel] Question about vcpu_avail
On 11/23/2009 04:28 PM, Keir Fraser wrote:
On 23/11/2009 15:02, "Michal Novotny"<minovotn@xxxxxxxxxx> wrote:
I would like to ask about vcpu_avail variable in XendDomainInfo.py. Is
that variable working and what is it used for ? I think it's a bitmask
showing what VCPUs are used and what are not, am I correct?
Yes, it allows you to configure which VCPUs are brought online by default on
guest bootup. If you do add a maxvcpus config item, it can be parsed out
into vcpus and vcpu_avail entirely within xm's create.py (excuse dodgy
pseudocode):
if defined(maxvcpus):
vcpu_avail = (1<< vcpus) - 1
vcpus = maxvcpus
i.e., no need for xend itself to know about the new config item.
-- Keir
Well, I don't know Keir since the main use scenario for maxvcpus is to
set number of vcpus for the guest so a new definition in Xend should be
required.
Then you just issue `xm vcpu-set {domainName} {numberOfVcpus}` command
to change number of VCPUs used by the guest, method `setVCpuCount(self,
vcpus)` from XendDomainInfo.py is called to set number of VCpus so check
should be implemented here as:
def setVCpuCount(self, vcpus):
if vcpus > self.info['maxvcpus']:
log.debug("Cannot set %d vcpu(s) for domain %s (domid %d)."
"Maximum number of vcpu(s) is set to %d" %
(vcpus, self.info['name'], self.domid,
self.info['maxvcpus']))
raise VmError("Cannot set %d vcpu(s). Maximum number of
vcpus for "
"this domain is %d" % (vcpus,
self.info['maxvcpus']) )
self.info['vcpu_avail'] = (1 << vcpus) - 1
self.storeVm('vcpu_avail', self.info['vcpu_avail'])
And domain_max_vcpus() call should be changed from
`xc.domain_max_vcpus(self.domid, int(self.info['vcpus']))` to
`xc.domain_max_vcpus(self.domid, int(self.info['maxvcpus']))`.
The only change that should be done to xm/create.py is to add `maxvcpus`
to add_conf mapping to allow it to be read/parsed out from the config file.
Well, I've been looking to the code and there is self.info['VCPUs_max']
in XendDomainInfo.py. What is it used for? Could it be used for the same
purpose like `maxvcpus` from example above?
Michal
Also, I'm
thinking of adding some variable of `maxvcpus` to define maximum number
of vcpus for PV guests. This way we could define a config file like:
vcpus = 2
maxvcpus = 4
and by setting `xm vcpu-set {domain} {numberOfVCPUs}` we can set up to 4
vcpus. Current behavior is to set to 1 vcpu and back to 2 vcpus but
never to cross the number defined in of vcpus. Now we could be able to
allocate up to 4 vcpus to the guest and not just 2... What do you think
about that idea?
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