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Date:   Thu, 26 Oct 2023 15:36:42 -0400
From:   Steven Rostedt <rostedt@goodmis.org>
To:     Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
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        Suleiman Souhlal <suleiman@google.com>,
        Ingo Molnar <mingo@kernel.org>,
        Daniel Bristot de Oliveira <bristot@kernel.org>
Subject: Re: [POC][RFC][PATCH v2] sched: Extended Scheduler Time Slice
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On Thu, 26 Oct 2023 14:59:13 -0400
Mathieu Desnoyers <mathieu.desnoyers@efficios.com> wrote:

> > Steven, check out
> > 
> >      arch/x86/include/asm/percpu.h
> > 
> > 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.

Thanks Linus and Mathieu!

Yeah, I just changed it to andb and that works just as well (or better).

When I first made the change, it became substantially worse. But then I
realized it was because I had "addb" and not "andb" :-D

-- Steve