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Date:   Fri, 27 Oct 2023 12:09:56 -0400
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Subject: Re: [POC][RFC][PATCH v2] sched: Extended Scheduler Time Slice
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To:     Steven Rostedt <rostedt@goodmis.org>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
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From:   Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
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On 2023-10-26 16:45, Steven Rostedt wrote:
> On Thu, 26 Oct 2023 14:59:13 -0400
> Mathieu Desnoyers <mathieu.desnoyers@efficios.com> wrote:
> 
>>> for a rough implementation of a 'xchg()' without SMP coherency, just
>>> cpu-local one (ie atomic wrt being preempted by the kernel, but not
>>> atomic wrt other CPU's accessing the same variable concurrently)
>>
>> Actually Steven does not need a xchg to test-and-set a single bit which
>> is only accessed concurrently between kernel and userspace from the same
>> thread. Either "bts" or "andb" should work fine.
> 
> Hmm, how would bts work? Doesn't that just set a bit?

Yes, and it saves the bit state in the CF flag before setting it.

If you need to clear a bit then it would be "btr".

> 
> I need to clear one bit while seeing if another bit is set. I could also
> use subl, as that would also atomically clear the bit.

Ah ok, I did not get that you needed to test for a different bit than 
the one you clear.

Thanks,

Mathieu

> 
> -- Steve

-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com