Re: [POC][RFC][PATCH v2] sched: Extended Scheduler Time Slice

[Mathieu Desnoyers]

On 2023-10-26 16:45, Steven Rostedt wrote:
> On Thu, 26 Oct 2023 14:59:13 -0400
> Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx> 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