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

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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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