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

[Jin, Yao]

On 4/24/2017 8:47 AM, 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?
> >
> > > +
> > > +    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

Hi,

Is this explanation OK? Since for tools part, it's Acked-by: Jiri Olsa. 
I just want to know  if the kernel part is OK either?

Thanks
Jin Yao