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

[Arnaldo Carvalho de Melo <acme@kernel.org>]

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