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

[Jin, Yao]

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?
>
> > +
> > +	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.

Thanks
Jin Yao

> > +
> > +		type >>= 1;
> > +	}
> > +
> > +	return PERF_BR_NONE;
> > +}
> > +
> >   /*