Messages in this thread |  | | Date | Sat, 10 Dec 2022 18:55:55 -0500 | From | Steven Rostedt <> | Subject | Re: [for-next][PATCH 13/25] x86/mm/kmmio: Use rcu_read_lock_sched_notrace() |
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On Sun, 11 Dec 2022 00:30:36 +0100 Thomas Gleixner <tglx@linutronix.de> wrote:
> On Sat, Dec 10 2022 at 13:34, Steven Rostedt wrote: > > On Sat, 10 Dec 2022 09:47:53 -0800 "Paul E. McKenney" <paulmck@kernel.org> wrote: > >> This does mess with preempt_count() redundantly, but the overhead from > >> that should be way down in the noise. > > > > I was going to remove it, but then I realized that it would be a functional > > change, as from the comment above, it uses "preempt_enable_no_resched(), > > which there is not a rcu_read_unlock_sched() variant. > > preempt_enable_no_resched() in this context is simply garbage. > > preempt_enable_no_resched() tries to avoid the overhead of checking > whether rescheduling is due after decrementing preempt_count() because > the code which it this claims to know that it is _not_ the outermost one > which brings preempt count back to preemtible state. > > I concede that there are hot paths which actually can benefit, but this > code has exactly _ZERO_ benefit from that. Taking that tracing exception > and handling it is orders of magnitudes more expensive than a regular > preempt_enable(). > > So just get rid of it and don't proliferate cargo cult programming. >
The point of the patch is to just fix the lockdep issue. I'm happy to remove that "no_resched" (I was planning to), but that would be a separate change, with a different purpose, and thus a separate patch.
-- Steve
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