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xen-users
Re: [Xen-users] VCPU amount
Dear Fajar A. Nugraha
please comment my mind:
so as i understand:
1. If i have only one domU and make 2 configs for it with vcpu=1 and
vcpu 8, the domu will have same perfomance, yes?
2. if i have 2 domu, one with vcpu=4 and second with vcpu=1, they will
have same perfomance if one of them is idle, and half of perfomance if
they are both loaded?
3. the only way to limit load is cpu_cap and for QOS is cpu_weight?
3. May be you mistake with:
In theory you can have something like a domU with vcpu=7 (note that
dom0 should have it's own dedicated core), cpu_weight=65000, and
cpu_cap=1, which should create a high-priority (cpu-wise) 7-way system
whose total performance equals to that of one cpu. It could be handy
for testing multi-threaded application to see how it performs in a
fast CPU vs many slow CPUs.
cpu_cap=1 - the system will have only 1% of 1 cpu power, may be mast
be cpu_cap=x*100 (x is a number of cpu for domu) for high-priority
(cpu-wise) %x-way system
ThankU!!!
PS sorry for my english
26 ÍÁÒÔÁ 2009, × 00:53, Fajar A. Nugraha ÎÁÐÉÓÁÌ(Á):
2009/3/26 Vladislav Karpenko <vladislav@xxxxxxxxxxxxxx>:
So there is two ways for domu cpu management vcpu and cpu_weight,
what is
the difference?
Three actually, with cpu_weight.
http://wiki.xensource.com/xenwiki/CreditScheduler
vcpu is the number of cpu on domU. If you have lots of cores and small
number of domUs, you might want to put each on a dedicated core (which
is similar to how Sun's LDOM work).
cpu_weight determines which domain will get higher priority when
fighting over the same cpu, while cpu_cap is max amount of cpu
resource it can use.
In theory you can have something like a domU with vcpu=7 (note that
dom0 should have it's own dedicated core), cpu_weight=65000, and
cpu_cap=1, which should create a high-priority (cpu-wise) 7-way system
whose total performance equals to that of one cpu. It could be handy
for testing multi-threaded application to see how it performs in a
fast CPU vs many slow CPUs.
Don't forget to check whether your xen version supports cpu_cap with
"xm create --help_config | grep cpu"
Regards,
Fajar
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