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

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Date:	Thu, 27 Sep 2012 15:37:42 +0530
From:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
To:	Konrad Rzeszutek Wilk <konrad@...nel.org>,
	Dor Laor <dlaor@...hat.com>
CC:	Chegu Vinod <chegu_vinod@...com>,
	Peter Zijlstra <peterz@...radead.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Ingo Molnar <mingo@...hat.com>, Avi Kivity <avi@...hat.com>,
	Rik van Riel <riel@...hat.com>,
	Srikar <srikar@...ux.vnet.ibm.com>,
	"Nikunj A. Dadhania" <nikunj@...ux.vnet.ibm.com>,
	KVM <kvm@...r.kernel.org>, Jiannan Ouyang <ouyang@...pitt.edu>,
	"Andrew M. Theurer" <habanero@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Srivatsa Vaddagiri <srivatsa.vaddagiri@...il.com>,
	Gleb Natapov <gleb@...hat.com>,
	Andrew Jones <drjones@...hat.com>
Subject: Re: [PATCH RFC 0/2] kvm: Improving undercommit,overcommit scenarios
 in PLE handler

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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