Re: [PATCH RFC 0/2] kvm: Improving undercommit,overcommit scenariosin PLE handler

[Raghavendra K T]

On 09/26/2012 05:57 PM, Konrad Rzeszutek Wilk wrote:
> On Tue, Sep 25, 2012 at 05:00:30PM +0200, Dor Laor wrote:
> > On 09/24/2012 02:02 PM, Raghavendra K T wrote:
> > > On 09/24/2012 02:12 PM, Dor Laor wrote:
> > > > In order to help PLE and pvticketlock converge I thought that a small
> > > > test code should be developed to test this in a predictable,
> > > > deterministic way.
> > > >
> > > > The idea is to have a guest kernel module that spawn a new thread each
> > > > time you write to a /sys/.... entry.
> > > >
> > > > Each such a thread spins over a spin lock. The specific spin lock is
> > > > also chosen by the /sys/ interface. Let's say we have an array of spin
> > > > locks *10 times the amount of vcpus.
> > > >
> > > > All the threads are running a
> > > > while (1) {
> > > >
> > > > spin_lock(my_lock);
> > > > sum += execute_dummy_cpu_computation(time);
> > > > spin_unlock(my_lock);
> > > >
> > > > if (sys_tells_thread_to_die()) break;
> > > > }
> > > >
> > > > print_result(sum);
> > > >
> > > > Instead of calling the kernel's spin_lock functions, clone them and make
> > > > the ticket lock order deterministic and known (like a linear walk of all
> > > > the threads trying to catch that lock).
> > >
> > > By Cloning you mean hierarchy of the locks?
> >
> > No, I meant to clone the implementation of the current spin lock
> > code in order to set any order you may like for the ticket
> > selection.
> > (even for a non pvticket lock version)
>
> Wouldn't that defeat the purpose of trying the test the different
> implementations that try to fix the lock-holder preemption problem?
> You want something that you can shoe-in for all work-loads - also
> for this test system.

Hmm true. I think it is indeed difficult to shoe-in all workloads.

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