linux-kernel - Re: [PATCH v8 2/7] perf/x86/intel: Record branch type

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Date:   Thu, 13 Jul 2017 16:31:50 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Jin Yao <yao.jin@...ux.intel.com>
Cc:     acme@...nel.org, jolsa@...nel.org, mingo@...hat.com,
        alexander.shishkin@...ux.intel.com, mpe@...erman.id.au,
        Linux-kernel@...r.kernel.org, ak@...ux.intel.com,
        kan.liang@...el.com, yao.jin@...el.com
Subject: Re: [PATCH v8 2/7] perf/x86/intel: Record branch type

On Thu, Jul 13, 2017 at 08:04:14PM +0800, Jin Yao wrote:
> +#define X86_BR_TYPE_MAP_MAX	16
> +
> +static int
> +common_branch_type(int type)
> +{
> +	int i, mask;
> +	const int branch_map[X86_BR_TYPE_MAP_MAX] = {
> +		PERF_BR_CALL,		/* X86_BR_CALL */
> +		PERF_BR_RET,		/* X86_BR_RET */
> +		PERF_BR_SYSCALL,	/* X86_BR_SYSCALL */
> +		PERF_BR_SYSRET,		/* X86_BR_SYSRET */
> +		PERF_BR_UNKNOWN,	/* X86_BR_INT */
> +		PERF_BR_UNKNOWN,	/* X86_BR_IRET */
> +		PERF_BR_COND,		/* X86_BR_JCC */
> +		PERF_BR_UNCOND,		/* X86_BR_JMP */
> +		PERF_BR_UNKNOWN,	/* X86_BR_IRQ */
> +		PERF_BR_IND_CALL,	/* X86_BR_IND_CALL */
> +		PERF_BR_UNKNOWN,	/* X86_BR_ABORT */
> +		PERF_BR_UNKNOWN,	/* X86_BR_IN_TX */
> +		PERF_BR_UNKNOWN,	/* X86_BR_NO_TX */
> +		PERF_BR_CALL,		/* X86_BR_ZERO_CALL */
> +		PERF_BR_UNKNOWN,	/* X86_BR_CALL_STACK */
> +		PERF_BR_IND,		/* X86_BR_IND_JMP */
> +	};
> +
> +	type >>= 2; /* skip X86_BR_USER and X86_BR_KERNEL */


> +	mask = ~(~0 << 1);

OCC worthy means of writing: 1

> +
> +	for (i = 0; i < X86_BR_TYPE_MAP_MAX; i++) {
> +		if (type & mask)
> +			return branch_map[i];
> +
> +		type >>= 1;
> +	}

That is some of the more confused code I've seen in a while :/

	if (type)
		return branch_map[__ffs(type)];

is what you meant to write, no?

> +
> +	return PERF_BR_UNKNOWN;
> +}