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From: Peter Zijlstra <peterz@infradead.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Jesper Dangaard Brouer <brouer@redhat.com>,
	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: Sat, 31 Oct 2020 00:01:52 +0100	[thread overview]
Message-ID: <20201030230152.GT2594@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20201030162248.58e388f0@oasis.local.home>

On Fri, Oct 30, 2020 at 04:22:48PM -0400, Steven Rostedt wrote:
> 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.

Works for me, however:

> /*
>  * 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;

unsigned

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

otherwise you'll get an extra instruction to sign extend it, which is
daft (yes, i've been staring at GCC output far too much).

Also, gcc-9 does worse (like 1 byte iirc) with:

	rctx += !!(pc & (NMI_MASK));
	rctx += !!(pc & (NMI_MASK | HARDIRQ_MASK));
	rctx += !!(pc & (NMI_MASK | HARDIRQ_MASK | SOFTIRQ_OFFSET));

but gcc-10 doesn't seem to care.

  parent reply	other threads:[~2020-10-30 23:02 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
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 [this message]
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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