linux-kernel - Re: [PATCH v6 2/7] perf/x86/intel: Record branch type

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Date:   Tue, 9 May 2017 10:26:44 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     "Jin, Yao" <yao.jin@...ux.intel.com>
Cc:     acme@...nel.org, jolsa@...nel.org, peterz@...radead.org,
        mingo@...hat.com, alexander.shishkin@...ux.intel.com,
        Linux-kernel@...r.kernel.org, ak@...ux.intel.com,
        kan.liang@...el.com, yao.jin@...el.com,
        linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v6 2/7] perf/x86/intel: Record branch type

On Mon, Apr 24, 2017 at 08:47:14AM +0800, Jin, Yao wrote:
> 
> 
> On 4/23/2017 9:55 PM, Jiri Olsa wrote:
> > On Thu, Apr 20, 2017 at 08:07:50PM +0800, Jin Yao wrote:
> > 
> > SNIP
> > 
> > > +#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_INT,		/* X86_BR_INT */
> > > +		PERF_BR_IRET,		/* X86_BR_IRET */
> > > +		PERF_BR_JCC,		/* X86_BR_JCC */
> > > +		PERF_BR_JMP,		/* X86_BR_JMP */
> > > +		PERF_BR_IRQ,		/* X86_BR_IRQ */
> > > +		PERF_BR_IND_CALL,	/* X86_BR_IND_CALL */
> > > +		PERF_BR_NONE,		/* X86_BR_ABORT */
> > > +		PERF_BR_NONE,		/* X86_BR_IN_TX */
> > > +		PERF_BR_NONE,		/* X86_BR_NO_TX */
> > > +		PERF_BR_CALL,		/* X86_BR_ZERO_CALL */
> > > +		PERF_BR_NONE,		/* X86_BR_CALL_STACK */
> > > +		PERF_BR_IND_JMP,	/* X86_BR_IND_JMP */
> > > +	};
> > > +
> > > +	type >>= 2; /* skip X86_BR_USER and X86_BR_KERNEL */
> > > +	mask = ~(~0 << 1);
> > is that a fancy way to get 1 into the mask? what do I miss?

you did not comment on this one

> > 
> > > +
> > > +	for (i = 0; i < X86_BR_TYPE_MAP_MAX; i++) {
> > > +		if (type & mask)
> > > +			return branch_map[i];
> > I wonder some bit search would be faster in here, but maybe not big deal
> > 
> > jirka
> 
> I just think the branch_map[] doesn't contain many entries (16 entries
> here), so maybe checking 1 bit one time should be acceptable. I just want to
> keep the code simple.
> 
> But if the number of entries is more (e.g. 64), maybe it'd better check 2 or
> 4 bits one time.

ook

jirka