Re: [PATCH v1 1/5] perf/core: Define the common branch type classification

Arnaldo Carvalho de Melo
2017-04-04T16:09:48Z

Em Tue, Apr 04, 2017 at 11:52:53PM +0800, Jin, Yao escreveu:
>
>
> On 4/4/2017 10:18 PM, Arnaldo Carvalho de Melo wrote:
> > Adding the perf kernel maintainers to the CC list.
> >
> > Em Fri, Mar 31, 2017 at 11:18:38PM +0800, Jin Yao escreveu:
> > > It is often useful to know the branch types while analyzing branch
> > > data. For example, a call is very different from a conditional branch.
> > >
> > > Currently we have to look it up in binary while the binary may later
> > > not be available and even the binary is available but user has to take
> > > some time. It is very useful for user to check it directly in perf
> > > report.
> > >
> > > Perf already has support for disassembling the branch instruction
> > > to get the branch type. The branch type is defined in lbr.c.
> > >
> > > To keep consistent on kernel and userspace and make the classification
> > > more common, the patch adds the common branch type classification
> > > in perf_event.h.
> > >
> > > Since the disassembling of branch instruction needs some overhead,
> > > a new PERF_SAMPLE_BRANCH_TYPE_SAVE is introduced to indicate if it
> > > needs to disassemble the branch instruction and record the branch
> > > type.
> > >
> > > Signed-off-by: Jin Yao <yao.jin@linux.intel.com>
> > > ---
> > > include/uapi/linux/perf_event.h | 24 +++++++++++++++++++++++-
> > > tools/include/uapi/linux/perf_event.h | 24 +++++++++++++++++++++++-
> > > 2 files changed, 46 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> > > index d09a9cd..4d731fd 100644
> > > --- a/include/uapi/linux/perf_event.h
> > > +++ b/include/uapi/linux/perf_event.h
> > > @@ -174,6 +174,8 @@ enum perf_branch_sample_type_shift {
> > > PERF_SAMPLE_BRANCH_NO_FLAGS_SHIFT = 14, /* no flags */
> > > PERF_SAMPLE_BRANCH_NO_CYCLES_SHIFT = 15, /* no cycles */
> > > + PERF_SAMPLE_BRANCH_TYPE_SAVE_SHIFT = 16, /* save branch type */
> > > +
> > > PERF_SAMPLE_BRANCH_MAX_SHIFT /* non-ABI */
> > > };
> > > @@ -198,9 +200,27 @@ enum perf_branch_sample_type {
> > > PERF_SAMPLE_BRANCH_NO_FLAGS = 1U << PERF_SAMPLE_BRANCH_NO_FLAGS_SHIFT,
> > > PERF_SAMPLE_BRANCH_NO_CYCLES = 1U << PERF_SAMPLE_BRANCH_NO_CYCLES_SHIFT,
> > > + PERF_SAMPLE_BRANCH_TYPE_SAVE =
> > > + 1U << PERF_SAMPLE_BRANCH_TYPE_SAVE_SHIFT,
> > > +
> > > PERF_SAMPLE_BRANCH_MAX = 1U << PERF_SAMPLE_BRANCH_MAX_SHIFT,
> > > };
> > > +/*
> > > + * Common flow change classification
> > > + */
> > > +enum {
> > > + PERF_BR_NONE = 0, /* unknown */
> > > + PERF_BR_JCC_FWD = 1 << 1, /* conditional forward jump */
> > > + PERF_BR_JCC_BWD = 1 << 2, /* conditional backward jump */
> > > + PERF_BR_JMP = 1 << 3, /* jump */
> > > + PERF_BR_IND_JMP = 1 << 4, /* indirect jump */
> > > + PERF_BR_CALL = 1 << 5, /* call */
> > > + PERF_BR_IND_CALL = 1 << 6, /* indirect call */
> > > + PERF_BR_RET = 1 << 7, /* return */
> > > + PERF_BR_FAR_BRANCH = 1 << 8, /* SYSCALL,SYSRET,IRQ,... */
> > Humm, wouldn't be better to have those in separate buckets? I.e.
> >
> > PERF_BR_SYSCALL
> > PERF_BR_SYSRET,
> > PERF_BR_IRQ
> >
> > etc?
>
> There are also other types. I.e. abort, ..... I use FAR_BRANCH is because I
> just want to differentiate between basic branch types and others. (others
> may be too much and platform specific).

I understand that this is what you need right now, but "syscall",
"sysret", "irq", look generic enough, no?

Really, really arch specific stuff could indeed be lumped together in a
FAR_BRANCH, but those used as an example, above (/*
SYSCALL,SYSRET,IRQ,... */) seems potentially useful to have untangled?

> > And why a bitmask? /me reads a bit more... couldn't find a reason for
> > this:
> >
> > + type:9, /* branch type */
> >
> > Do you have a reason to use 9 bits? Why not just:
> >
> > enum {
> > PERF_BR_NONE = 0, /* unknown */
> > PERF_BR_JCC_FWD = 1, /* conditional forward jump */
> > PERF_BR_JCC_BWD = 2, /* conditional backward jump */
> > PERF_BR_JMP = 3, /* jump */
> > PERF_BR_IND_JMP = 4, /* indirect jump */
> > PERF_BR_CALL = 5, /* call */
> > PERF_BR_IND_CALL = 6, /* indirect call */
> > PERF_BR_RET = 7, /* return */
> > PERF_BR_FAR_BRANCH = 8, /* SYSCALL,SYSRET,IRQ,... */
> >
> > And then use, say, 4 or 5 bits for that type field?
> >
> > I must be missing something trivial ;-\
> >
> > - Arnaldo
>
> You are right. I made things more complicated. Yes, the definitions should
> be clear and simple. I will redefine them in v2.

Thanks, I wasn't missing anything, uff :-)

> Thanks
> Jin Yao
>
> >
> > > +};
> > > +
> > > #define PERF_SAMPLE_BRANCH_PLM_ALL \
> > > (PERF_SAMPLE_BRANCH_USER|\
> > > PERF_SAMPLE_BRANCH_KERNEL|\
> > > @@ -999,6 +1019,7 @@ union perf_mem_data_src {
> > > * in_tx: running in a hardware transaction
> > > * abort: aborting a hardware transaction
> > > * cycles: cycles from last branch (or 0 if not supported)
> > > + * type: branch type
> > > */
> > > struct perf_branch_entry {
> > > __u64 from;
> > > @@ -1008,7 +1029,8 @@ struct perf_branch_entry {
> > > in_tx:1, /* in transaction */
> > > abort:1, /* transaction abort */
> > > cycles:16, /* cycle count to last branch */
> > > - reserved:44;
> > > + type:9, /* branch type */
> > > + reserved:35;
> > > };
> > > #endif /* _UAPI_LINUX_PERF_EVENT_H */
> > > diff --git a/tools/include/uapi/linux/perf_event.h b/tools/include/uapi/linux/perf_event.h
> > > index d09a9cd..4d731fd 100644
> > > --- a/tools/include/uapi/linux/perf_event.h
> > > +++ b/tools/include/uapi/linux/perf_event.h
> > > @@ -174,6 +174,8 @@ enum perf_branch_sample_type_shift {
> > > PERF_SAMPLE_BRANCH_NO_FLAGS_SHIFT = 14, /* no flags */
> > > PERF_SAMPLE_BRANCH_NO_CYCLES_SHIFT = 15, /* no cycles */
> > > + PERF_SAMPLE_BRANCH_TYPE_SAVE_SHIFT = 16, /* save branch type */
> > > +
> > > PERF_SAMPLE_BRANCH_MAX_SHIFT /* non-ABI */
> > > };
> > > @@ -198,9 +200,27 @@ enum perf_branch_sample_type {
> > > PERF_SAMPLE_BRANCH_NO_FLAGS = 1U << PERF_SAMPLE_BRANCH_NO_FLAGS_SHIFT,
> > > PERF_SAMPLE_BRANCH_NO_CYCLES = 1U << PERF_SAMPLE_BRANCH_NO_CYCLES_SHIFT,
> > > + PERF_SAMPLE_BRANCH_TYPE_SAVE =
> > > + 1U << PERF_SAMPLE_BRANCH_TYPE_SAVE_SHIFT,
> > > +
> > > PERF_SAMPLE_BRANCH_MAX = 1U << PERF_SAMPLE_BRANCH_MAX_SHIFT,
> > > };
> > > +/*
> > > + * Common flow change classification
> > > + */
> > > +enum {
> > > + PERF_BR_NONE = 0, /* unknown */
> > > + PERF_BR_JCC_FWD = 1 << 1, /* conditional forward jump */
> > > + PERF_BR_JCC_BWD = 1 << 2, /* conditional backward jump */
> > > + PERF_BR_JMP = 1 << 3, /* jump */
> > > + PERF_BR_IND_JMP = 1 << 4, /* indirect jump */
> > > + PERF_BR_CALL = 1 << 5, /* call */
> > > + PERF_BR_IND_CALL = 1 << 6, /* indirect call */
> > > + PERF_BR_RET = 1 << 7, /* return */
> > > + PERF_BR_FAR_BRANCH = 1 << 8, /* SYSCALL,SYSRET,IRQ,... */
> > > +};
> > > +
> > > #define PERF_SAMPLE_BRANCH_PLM_ALL \
> > > (PERF_SAMPLE_BRANCH_USER|\
> > > PERF_SAMPLE_BRANCH_KERNEL|\
> > > @@ -999,6 +1019,7 @@ union perf_mem_data_src {
> > > * in_tx: running in a hardware transaction
> > > * abort: aborting a hardware transaction
> > > * cycles: cycles from last branch (or 0 if not supported)
> > > + * type: branch type
> > > */
> > > struct perf_branch_entry {
> > > __u64 from;
> > > @@ -1008,7 +1029,8 @@ struct perf_branch_entry {
> > > in_tx:1, /* in transaction */
> > > abort:1, /* transaction abort */
> > > cycles:16, /* cycle count to last branch */
> > > - reserved:44;
> > > + type:9, /* branch type */
> > > + reserved:35;
> > > };
> > > #endif /* _UAPI_LINUX_PERF_EVENT_H */
> > > --
> > > 2.7.4