[nova][scheduler] - Stack VMs based on RAM
On Thu, 2019-04-18 at 01:38 +0100, Sean Mooney wrote:
> On Wed, 2019-04-17 at 15:30 -0700, melanie witt wrote:
> > On Thu, 18 Apr 2019 01:13:42 +0300, Georgios Dimitrakakis
> > <giorgis at acmac.uoc.gr> wrote:
> > > Shouldnâ??t that be the correct behavior and place the new VM on the host with the smaller weight? Isnâ??t that what
> > > the
> > > negative value for â??ram_weight_multiplierâ?? does ?
> > No, it's the opposite, higher weights win. That's why you have to use a
> > negative value for ram_weight_multiplier if you want hosts with _less_
> > RAM to win over hosts with more RAM (stacking).
> > > Please let me know how I can provide to you more debug info....
> > One thing I noticed from your log is on the second request, 'cpu1' has
> > io_ops: 0 whereas 'cpu2' has io_ops: 1 and the IoOpsWeigher  will
> > prefer hosts with fewer io_iops by default. Note that's only one piece
> > of the ending weight -- the weighing process will take a sum of all of
> > the weights each weigher returns. So the weight returned from RamWeigher
> > is added to the weight returned from IoOpsWeigher is added the weight
> > returned from CPUWeigher, and so on.
> > So, as Matt said, we're a bit in the dark now as far as what each
> > weigher is returning and we don't currently have debug logging per
> > weigher the way we do for filters. That would be an enhancement we could
> > make to aid in debugging issues like this one. You could hack something
> > up locally to log/print the returned weight in each weight class under
> > the nova/scheduler/weights/ directory, if you want to dig into that.
> > Another thing I noticed is that there are probably some new weighers
> > available by default that did not exist in the previous version of nova
> > that you were using in the past. By default, the config option for weighers:
> > [filter_scheduler]weight_classes = ["nova.scheduler.weights.all_weighers"]
> > will pick up all weigher classes in the nova/scheduler/weights/ code
> > directory. You might take a look at these and see if any are ones you
> > should exclude in your environment. For example, the CPUWeigher  (new
> > in Rocky) will spread VMs based on available CPU by default.
> most of the weighers spread by default so the cpu weigher may be a factor but
> the the disk weigher tends to all hevily impact the choice.
> we do not normalise any of the values retured by the different weighers
> the disk wighter is basically host_state.free_disk_mb * disk_weight_multiplier
> althoer host_state.free_disk_mb is actully disk_available_least.
> as a result the disk filter will weigh cpu1 19456 height then cpu2
> the dela between the cpu1 and cpu2 based on the ram weigher is only 2048
> if you want the ram filter to take presedence over teh disk filter you will
> need to scale the disk filter down to be in a similar value range
> i woudl suggest setting disk_weight_multiplier=0.001
actully based on
we do nomalise however i have had issues with this in the past where i have had to re addjsut the weights
to effectivly renomalise the different weighers.
disk_weight_multiplier=0.001 is proably a little extream
> > This
> > weigher might be contributing to the VM spreading you're seeing. You
> > might try playing with the '[filter_scheduler]weight_classes' config
> > option to select only the weighers you want or alternatively you could
> > set the weighers multipliers the way you prefer.
> > -melanie
> >  https://docs.openstack.org/nova/rocky/user/filter-scheduler.html#weights
> > > > > On 4/17/2019 3:50 PM, Georgios Dimitrakakis wrote:
> > > > > And here is the new log where spawning of 2 VMs can be seen with a few seconds of difference:
> > > > > https://pastebin.com/Xy2FL2KL
> > > > > Initially both hosts are of weight 1.0 then the one with one VM already running has negative weight but the
> > > > > new
> > > > > VM is placed on the other host.
> > > > > Really-really strange why this is happening...
> > > >
> > > > < 2019-04-17 23:26:18.770 157355 DEBUG nova.scheduler.filter_scheduler [req-14c666e4-3ff4-4d88-947e-377b3d37bff9
> > > > 6a4c2e32919e4a6fa5c5d956beb68eef 9f22e9bfa7974e14871d58bbb62242b2 - default default] Filtered [(cpu2, cpu2) ram:
> > > > 30105MB disk: 1887232MB io_ops: 1 instances: 1, (cpu1, cpu1) ram: 32153MB disk: 1906688MB io_ops: 0 instances:
> > > > 0]
> > > > _get_sorted_hosts /usr/lib/python2.7/site-packages/nova/scheduler/filter_scheduler.py:435
> > > >
> > > > < 2019-04-17 23:26:18.771 157355 DEBUG nova.scheduler.filter_scheduler [req-14c666e4-3ff4-4d88-947e-377b3d37bff9
> > > > 6a4c2e32919e4a6fa5c5d956beb68eef 9f22e9bfa7974e14871d58bbb62242b2 - default default] Weighed [WeighedHost [host:
> > > > (cpu1, cpu1) ram: 32153MB disk: 1906688MB io_ops: 0 instances: 0, weight: 1.0], WeighedHost [host: (cpu2, cpu2)
> > > > ram: 30105MB disk: 1887232MB io_ops: 1 instances: 1, weight: -0.00900862553213]] _get_sorted_hosts
> > > > /usr/lib/python2.7/site-packages/nova/scheduler/filter_scheduler.py:454
> > > >
> > > > cpu1 is definitely getting weighed higher but I'm not sure why. We likely need some debug logging on the result
> > > > of
> > > > each weigher like we have for each filter to figure out what's going on with the weighers.
> > > >
> > > > --
> > > >
> > > > Thanks,
> > > >
> > > > Matt