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Hi Boris,
I am still getting my feet wet with rally so some concepts are new, and did not quite get your statement regarding the different load generators. I am presuming you are referring to the Scenario runner and the different “types” of runs.

What I was looking at is the runner, where we specify the type, times and concurrency.  We could have an additional field(s) which would specify the synchronization property.

Essentially, what I have found most useful in the cases where we run scenarios/tests in parallel;  is some sort of “barrier”, where at a certain point in the run you want all the parallel tasks to reach a specific point before continuing.

Also, I am also considering cases where synchronization is needed within a single benchmark case, where the same benchmark scenario:
creates some vms, performs some tasks, deletes the vm

Just for simplicity as a POC, I tried something with shared memory (multiprocessing.Value), which looks something like this:

class Barrier(object):
    __init__(self, concurrency)
        self.shmem = multiprocessing.Value(‘I’, concurrency)
        self.lock = multiprocessing.Lock()

    def wait_at_barrier ():
       while self.shmem.value > 0:
           time.sleep(1)
       return

    def decrement_shm_concurrency_cnt ():
         with self.lock:
             self.shmem.value -=  1


And from the scenario, it can be called as:

scenario:
 -- do some action –
  barrobj.decrement_shm_concurrency_cnt()
 sync_helper.wait_at_barrier()
-- do some action –   <-- all processes will do this action at almost the same time.

I would be happy to discuss more to get a good common solution.

regards,
Behzad





From: boris at pavlovic.ru [mailto:boris at pavlovic.ru] On Behalf Of Boris Pavlovic
Sent: Tuesday, October 21, 2014 3:23 PM
To: Behzad Dastur (bdastur)
Cc: OpenStack Development Mailing List (not for usage questions); Pradeep Chandrasekar (pradeech); John Wei-I Wu (weiwu)
Subject: Re: [openstack-dev] [rally][users]: Synchronizing between multiple scenario instances.

Behzad,

Unfortunately at this point there is no support of locking between scenarios.


It will be quite tricky for implementation, because we have different load generators, and we will need to find
common solutions for all of them.

If you have any ideas about how to implement it in such way, I will be more than happy to get this in upstream.


One of the way that I see is to having some kind of chain-of-benchmarks:

1) Like first benchmark is running N VMs
2) Second benchmarking is doing something with all those benchmarks
3) Third benchmark is deleting all these VMs

(where chain elements are atomic actions)

Probably this will be better long term solution.
Only thing that we should understand is how to store those results and how to display them.


If you would like to help with this let's start discussing it, in some kind of google docs.

Thoughts?


Best regards,
Boris Pavlovic


On Wed, Oct 22, 2014 at 2:13 AM, Behzad Dastur (bdastur) <bdastur at cisco.com<mailto:bdastur at cisco.com>> wrote:
Does rally provide any synchronization mechanism to synchronize between multiple scenario, when running in parallel? Rally spawns multiple processes, with each process running the scenario.  We need a way to synchronize between these to start a perf test operation at the same time.


regards,
Behzad


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