linux-kernel - Re: [PATCH 2/5] perf core: Set event's default overflow

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Date:	Wed, 23 Mar 2016 18:50:21 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Wang Nan <wangnan0@...wei.com>
Cc:	mingo@...hat.com, linux-kernel@...r.kernel.org,
	He Kuang <hekuang@...wei.com>,
	Alexei Starovoitov <ast@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Brendan Gregg <brendan.d.gregg@...il.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Zefan Li <lizefan@...wei.com>, pi3orama@....com,
	Will Deacon <will.deacon@....com>
Subject: Re: [PATCH 2/5] perf core: Set event's default overflow_handler

On Mon, Mar 14, 2016 at 09:59:42AM +0000, Wang Nan wrote:
> +++ b/arch/arm/kernel/hw_breakpoint.c
> @@ -631,7 +631,7 @@ int arch_validate_hwbkpt_settings(struct perf_event *bp)
>  	info->address &= ~alignment_mask;
>  	info->ctrl.len <<= offset;
>  
> -	if (!bp->overflow_handler) {
> +	if (is_default_overflow_handler(bp)) {
>  		/*
>  		 * Mismatch breakpoints are required for single-stepping
>  		 * breakpoints.
> @@ -754,7 +754,7 @@ static void watchpoint_handler(unsigned long addr, unsigned int fsr,
>  		 * mismatch breakpoint so we can single-step over the
>  		 * watchpoint trigger.
>  		 */
> -		if (!wp->overflow_handler)
> +		if (is_default_overflow_handler(wp))
>  			enable_single_step(wp, instruction_pointer(regs));
>  
>  unlock:
> diff --git a/arch/arm64/kernel/hw_breakpoint.c b/arch/arm64/kernel/hw_breakpoint.c
> index b45c95d..4ef5373 100644
> --- a/arch/arm64/kernel/hw_breakpoint.c
> +++ b/arch/arm64/kernel/hw_breakpoint.c
> @@ -616,7 +616,7 @@ static int breakpoint_handler(unsigned long unused, unsigned int esr,
>  		perf_bp_event(bp, regs);
>  
>  		/* Do we need to handle the stepping? */
> -		if (!bp->overflow_handler)
> +		if (is_default_overflow_handler(bp))
>  			step = 1;
>  unlock:
>  		rcu_read_unlock();
> @@ -712,7 +712,7 @@ static int watchpoint_handler(unsigned long addr, unsigned int esr,
>  		perf_bp_event(wp, regs);
>  
>  		/* Do we need to handle the stepping? */
> -		if (!wp->overflow_handler)
> +		if (is_default_overflow_handler(wp))
>  			step = 1;
>  
>  unlock:

Will, why does it matter what the overflow handler is for this stuff?