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

[Jin, Yao]

On 7/13/2017 11:06 PM, Jin, Yao wrote:
> Sorry, please ignore my previous response.
>
>
> On 7/13/2017 10:31 PM, Peter Zijlstra wrote:
> > 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?
>
> Now I understand what you suggest. Yes, that's right.
>
> Do I need to update the patch?
>
> Thanks
> Jin Yao

Looks it should be:

if (type)
    return branch_map[__ffs(type) - 1];

> > > +
> > > +    return PERF_BR_UNKNOWN;
> > > +}