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Date:	Wed, 05 Mar 2014 17:02:50 -0700
From:	Khalid Aziz <>
To:	"H. Peter Anvin" <>, David Lang <>
CC:	Oleg Nesterov <>, Andi Kleen <>,
	Thomas Gleixner <>,
	One Thousand Gnomes <>,
	Ingo Molnar <>,,,,
Subject: Re: [RFC] [PATCH] Pre-emption control for userspace

On 03/05/2014 04:56 PM, H. Peter Anvin wrote:
> On 03/05/2014 03:48 PM, Khalid Aziz wrote:
>> Cost is writing to a memory location since thread is using mmap, not
>> insignificant but hardly expensive. Thread does not need to know how
>> much time it has left in current timeslice. It always sets the flag to
>> request pre-emption immunity before entering the critical section and
>> clears the flag when it exits its critical section. If the thread comes
>> up for pre-emption while the flag is set, it gets immunity. If it does
>> not, flag will be cleared at the end of critical section any way.
> A little more than that.  The scheduler needs to set *another* flag
> telling the process to yield upon leaving the critical section; if the
> process doesn't, the scheduler needs to keep enough accounting to know
> to penalize the process, or this method will not be usable for
> unprivileged processes.

Yes, you had made that suggestion earlier and I like it. It will be in 
v2 patch. I am thinking of making the penalty be denial of next 
preemption immunity request if a process fails to yield when it should 
have. Sounds good?

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