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From: Steven Rostedt <rostedt@goodmis.org>
To: Jesper Dangaard Brouer <brouer@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	mingo@kernel.org, tglx@linutronix.de,
	linux-kernel@vger.kernel.org, kan.liang@linux.intel.com,
	acme@kernel.org, mark.rutland@arm.com,
	alexander.shishkin@linux.intel.com, jolsa@redhat.com,
	namhyung@kernel.org, ak@linux.intel.com, eranian@google.com
Subject: Re: [PATCH 4/6] perf: Optimize get_recursion_context()
Date: Fri, 30 Oct 2020 16:22:48 -0400	[thread overview]
Message-ID: <20201030162248.58e388f0@oasis.local.home> (raw)
In-Reply-To: <20201030181138.215b2b6a@carbon>

On Fri, 30 Oct 2020 18:11:38 +0100
Jesper Dangaard Brouer <brouer@redhat.com> wrote:

> On Fri, 30 Oct 2020 16:13:49 +0100
> Peter Zijlstra <peterz@infradead.org> wrote:
> 
> >   "Look ma, no branches!"
> > 
> > Cc: Jesper Dangaard Brouer <brouer@redhat.com>
> > Cc: Steven Rostedt <rostedt@goodmis.org>
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> > ---  
> 
> Cool trick! :-)
> 
> Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>
> 
> >  kernel/events/internal.h |   17 ++++++++---------
> >  1 file changed, 8 insertions(+), 9 deletions(-)
> > 
> > --- a/kernel/events/internal.h
> > +++ b/kernel/events/internal.h
> > @@ -205,16 +205,15 @@ DEFINE_OUTPUT_COPY(__output_copy_user, a
> >  
> >  static inline int get_recursion_context(int *recursion)
> >  {
> > -	int rctx;
> > +	unsigned int pc = preempt_count();
> > +	unsigned int rctx = 0;
> >  
> > -	if (unlikely(in_nmi()))
> > -		rctx = 3;
> > -	else if (in_irq())
> > -		rctx = 2;
> > -	else if (in_serving_softirq())
> > -		rctx = 1;
> > -	else
> > -		rctx = 0;
> > +	if (pc & (NMI_MASK))
> > +		rctx++;
> > +	if (pc & (NMI_MASK | HARDIRQ_MASK))
> > +		rctx++;
> > +	if (pc & (NMI_MASK | HARDIRQ_MASK | SOFTIRQ_OFFSET))
> > +		rctx++;
> >  
> >  	if (recursion[rctx])
> >  		return -1;
> > 
> > 

As this is something that ftrace recursion also does, perhaps we should
move this into interrupt.h so that anyone that needs a counter can get
it quickly, and not keep re-implementing it.

/*
 * Quickly find what context you are in.
 * 0 - normal
 * 1 - softirq
 * 2 - hard interrupt
 * 3 - NMI
 */
static inline int irq_context()
{
	unsigned int pc = preempt_count();
	int rctx = 0;

	if (pc & (NMI_MASK))
		rctx++;
	if (pc & (NMI_MASK | HARDIRQ_MASK))
		rctx++;
	if (pc & (NMI_MASK | HARDIRQ_MASK | SOFTIRQ_OFFSET))
		rctx++;

	return rctx;
}

-- Steve

  reply	other threads:[~2020-10-30 20:22 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-30 15:13 [PATCH 0/6] perf: Reduce stack usage (and misc bits) Peter Zijlstra
2020-10-30 15:13 ` [PATCH 1/6] perf: Reduce stack usage of perf_output_begin() Peter Zijlstra
2020-11-10 12:45   ` [tip: perf/urgent] " tip-bot2 for Peter Zijlstra
2020-10-30 15:13 ` [PATCH 2/6] perf/x86: Reduce stack usage for x86_pmu::drain_pebs() Peter Zijlstra
2020-11-10 12:45   ` [tip: perf/urgent] " tip-bot2 for Peter Zijlstra
2020-10-30 15:13 ` [PATCH 3/6] perf: Fix get_recursion_context() Peter Zijlstra
2020-11-10 12:45   ` [tip: perf/urgent] " tip-bot2 for Peter Zijlstra
2020-10-30 15:13 ` [PATCH 4/6] perf: Optimize get_recursion_context() Peter Zijlstra
2020-10-30 17:11   ` Jesper Dangaard Brouer
2020-10-30 20:22     ` Steven Rostedt [this message]
2020-10-30 22:14       ` Thomas Gleixner
2020-10-30 23:31         ` Steven Rostedt
2020-10-31 11:23           ` Peter Zijlstra
2020-10-30 23:01       ` Peter Zijlstra
2020-10-31 12:11         ` David Laight
2020-10-31 13:18           ` David Laight
2020-11-09 12:12           ` Peter Zijlstra
2020-11-09 14:14             ` David Laight
2020-11-10 12:45   ` [tip: perf/urgent] " tip-bot2 for Peter Zijlstra
2020-10-30 15:13 ` [PATCH 5/6] perf/arch: Remove perf_sample_data::regs_user_copy Peter Zijlstra
2020-11-10 12:45   ` [tip: perf/urgent] " tip-bot2 for Peter Zijlstra
2020-10-30 15:13 ` [PATCH 6/6] perf/x86: Make dummy_iregs static Peter Zijlstra
2020-11-10 12:45   ` [tip: perf/urgent] " tip-bot2 for Peter Zijlstra

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