Messages in this thread | | | From | Thomas Gleixner <> | Subject | Re: [patch V2 2/9] irqtime: Make accounting correct on RT | Date | Mon, 07 Dec 2020 15:44:28 +0100 |
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On Mon, Dec 07 2020 at 14:27, Frederic Weisbecker wrote: > On Fri, Dec 04, 2020 at 06:01:53PM +0100, Thomas Gleixner wrote: >> vtime_account_irq and irqtime_account_irq() base checks on preempt_count() >> which fails on RT because preempt_count() does not contain the softirq >> accounting which is seperate on RT. >> >> These checks do not need the full preempt count as they only operate on the >> hard and softirq sections. >> >> Use irq_count() instead which provides the correct value on both RT and non >> RT kernels. The compiler is clever enough to fold the masking for !RT: >> >> 99b: 65 8b 05 00 00 00 00 mov %gs:0x0(%rip),%eax >> - 9a2: 25 ff ff ff 7f and $0x7fffffff,%eax >> + 9a2: 25 00 ff ff 00 and $0xffff00,%eax >> >> Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> >> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> > > Reviewed-by: Frederic Weisbecker <frederic@kernel.org> > > Also I'm seeing a few other explicit SOFTIRQ_MASK checks on top > of preempt_count(), especially on RCU: > > $ git grep SOFTIRQ_MASK > arch/sh/kernel/irq.c: (irqctx->tinfo.preempt_count & ~SOFTIRQ_MASK) | > arch/sh/kernel/irq.c: (curctx->tinfo.preempt_count & SOFTIRQ_MASK); > kernel/rcu/rcutorture.c: if (preempt_count() & (SOFTIRQ_MASK | HARDIRQ_MASK)) > kernel/rcu/tree_exp.h: if (!(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK)) || > kernel/rcu/tree_plugin.h: !!(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK)); > kernel/rcu/tree_plugin.h: (preempt_count() & > (PREEMPT_MASK | SOFTIRQ_MASK))) { > > I guess some RT RCU config take care of that?
I ignored sh so far and RCU has some quirks for RT vs. softirqs.
> Also tracing: > > kernel/trace/ring_buffer.c: if (!(pc & (NMI_MASK | HARDIRQ_MASK | SOFTIRQ_OFFSET))) > kernel/trace/trace.c: ((pc & SOFTIRQ_OFFSET) ? TRACE_FLAG_SOFTIRQ : 0)
Bah, I somehow lost the cure for that while rebasing.
Thanks,
tglx
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