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SubjectRe: [PATCH v7 07/18] perf: add generic memory sampling interface
> 
> * Stephane Eranian <eranian@google.com> wrote:
>
> > This patch adds PERF_SAMPLE_DSRC.
> >
> > PERF_SAMPLE_DSRC collects the data source, i.e., where
> > did the data associated with the sampled instruction
> > come from. Information is stored in a perf_mem_dsrc
> > structure. It contains opcode, mem level, tlb, snoop,
> > lock information, subject to availability in hardware.
> >
> > Signed-off-by: Stephane Eranian <eranian@google.com>
> > ---
> > include/linux/perf_event.h | 2 ++
> > include/uapi/linux/perf_event.h | 68 +++++++++++++++++++++++++++++++++++++--
> > kernel/events/core.c | 6 ++++
> > 3 files changed, 74 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> > index bb2429d..8fe4610 100644
> > --- a/include/linux/perf_event.h
> > +++ b/include/linux/perf_event.h
> > @@ -579,6 +579,7 @@ struct perf_sample_data {
> > u32 reserved;
> > } cpu_entry;
> > u64 period;
> > + union perf_mem_dsrc dsrc;
> > struct perf_callchain_entry *callchain;
> > struct perf_raw_record *raw;
> > struct perf_branch_stack *br_stack;
> > @@ -599,6 +600,7 @@ static inline void perf_sample_data_init(struct perf_sample_data *data,
> > data->regs_user.regs = NULL;
> > data->stack_user_size = 0;
> > data->weight = 0;
> > + data->dsrc.val = 0;
> > }
> >
> > extern void perf_output_sample(struct perf_output_handle *handle,
> > diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> > index 3e6c394..3e4844c 100644
> > --- a/include/uapi/linux/perf_event.h
> > +++ b/include/uapi/linux/perf_event.h
> > @@ -133,9 +133,9 @@ enum perf_event_sample_format {
> > PERF_SAMPLE_REGS_USER = 1U << 12,
> > PERF_SAMPLE_STACK_USER = 1U << 13,
> > PERF_SAMPLE_WEIGHT = 1U << 14,
> > + PERF_SAMPLE_DSRC = 1U << 15,
> >
> > - PERF_SAMPLE_MAX = 1U << 15, /* non-ABI */
> > -
> > + PERF_SAMPLE_MAX = 1U << 16, /* non-ABI */
> > };
> >
> > /*
> > @@ -591,6 +591,7 @@ enum perf_event_type {
> > * u64 dyn_size; } && PERF_SAMPLE_STACK_USER
> > *
> > * { u64 weight; } && PERF_SAMPLE_WEIGHT
> > + * { u64 dsrc; } && PERF_SAMPLE_DSRC
> > * };
> > */
> > PERF_RECORD_SAMPLE = 9,
> > @@ -616,4 +617,67 @@ enum perf_callchain_context {
> > #define PERF_FLAG_FD_OUTPUT (1U << 1)
> > #define PERF_FLAG_PID_CGROUP (1U << 2) /* pid=cgroup id, per-cpu mode only */
> >
> > +union perf_mem_dsrc {
> > + __u64 val;
> > + struct {
> > + __u64 mem_op:5, /* type of opcode */
> > + mem_lvl:14, /* memory hierarchy level */
> > + mem_snoop:5, /* snoop mode */
> > + mem_lock:2, /* lock instr */
> > + mem_dtlb:7, /* tlb access */
> > + mem_rsvd:31;
> > + };


POWER could use an additional field:

mem_deratmiss:1

AFAICT, POWER does not currently save the mem_op, snoop or lock info
for the sampled instruction. I guess we can leave them set to 0.

> > +};
> > +
> > +/* type of opcode (load/store/prefetch,code) */
> > +#define PERF_MEM_OP_NA 0x01 /* not available */
> > +#define PERF_MEM_OP_LOAD 0x02 /* load instruction */
> > +#define PERF_MEM_OP_STORE 0x04 /* store instruction */
> > +#define PERF_MEM_OP_PFETCH 0x08 /* prefetch */
> > +#define PERF_MEM_OP_EXEC 0x10 /* code (execution) */
> > +#define PERF_MEM_OP_SHIFT 0
> > +
> > +/* memory hierarchy (memory level, hit or miss) */
> > +#define PERF_MEM_LVL_NA 0x01 /* not available */
> > +#define PERF_MEM_LVL_HIT 0x02 /* hit level */
> > +#define PERF_MEM_LVL_MISS 0x04 /* miss level */
> > +#define PERF_MEM_LVL_L1 0x08 /* L1 */
> > +#define PERF_MEM_LVL_LFB 0x10 /* Line Fill Buffer */
> > +#define PERF_MEM_LVL_L2 0x20 /* L2 hit */
> > +#define PERF_MEM_LVL_L3 0x40 /* L3 hit */
> > +#define PERF_MEM_LVL_LOC_RAM 0x80 /* Local DRAM */
> > +#define PERF_MEM_LVL_REM_RAM1 0x100 /* Remote DRAM (1 hop) */
> > +#define PERF_MEM_LVL_REM_RAM2 0x200 /* Remote DRAM (2 hops) */
> > +#define PERF_MEM_LVL_REM_CCE1 0x400 /* Remote Cache (1 hop) */
> > +#define PERF_MEM_LVL_REM_CCE2 0x800 /* Remote Cache (2 hops) */
> > +#define PERF_MEM_LVL_IO 0x1000 /* I/O memory */
> > +#define PERF_MEM_LVL_UNC 0x2000 /* Uncached memory */
> > +#define PERF_MEM_LVL_SHIFT 5

POWER saves following information to describe where the data was loaded from
after a Dcache or DTLB miss.

FROM_L2
FROM_L3

FROM_L2.1_SHR From another L2 or L3 on same chip, shared
FROM_L2.1_MOD From another L2 or L3 on same chip, modified

FROM_L3.1_SHR From remote L2 or L3, shared
FROM_L3.1_MOD From remote L2 or L3, modified

FROM_RL2L3_SHR From remote L2 or L3, shared
FROM_RL2L3_MOD From remote L2 or L3, modified

FROM_DL2L3_SHR From distant L2 or L3, shared
FROM_DL2L3_MOD From distant L2 or L3, modified

POWER uses 4 bits and a running count for its (currently) 13 possible values.

The macros in the patch use a separate bit for each level - is that to allow
selecting more than one level at the same time ? If so, we will need to reserve
a few more bits to allow for Power's memory levels that don't map to the above.

> > +
> > +/* snoop mode */
> > +#define PERF_MEM_SNOOP_NA 0x01 /* not available */
> > +#define PERF_MEM_SNOOP_NONE 0x02 /* no snoop */
> > +#define PERF_MEM_SNOOP_HIT 0x04 /* snoop hit */
> > +#define PERF_MEM_SNOOP_MISS 0x08 /* snoop miss */
> > +#define PERF_MEM_SNOOP_HITM 0x10 /* snoop hit modified */
> > +#define PERF_MEM_SNOOP_SHIFT 19
> > +
> > +/* locked instruction */
> > +#define PERF_MEM_LOCK_NA 0x01 /* not available */
> > +#define PERF_MEM_LOCK_LOCKED 0x02 /* locked transaction */
> > +#define PERF_MEM_LOCK_SHIFT 24
> > +
> > +/* TLB access */
> > +#define PERF_MEM_TLB_NA 0x01 /* not available */
> > +#define PERF_MEM_TLB_HIT 0x02 /* hit level */
> > +#define PERF_MEM_TLB_MISS 0x04 /* miss level */
> > +#define PERF_MEM_TLB_L1 0x08 /* L1 */
> > +#define PERF_MEM_TLB_L2 0x10 /* L2 */
> > +#define PERF_MEM_TLB_WK 0x20 /* Hardware Walker*/
> > +#define PERF_MEM_TLB_OS 0x40 /* OS fault handler */
> > +#define PERF_MEM_TLB_SHIFT 26

On POWER, like with the Dcache source above, we have 4 bits to describe where
the DTLB was loaded from after a dTLB miss.

We would probably need to allow more bits to for the memory level of the dTLB
load source.

> > +
> > +#define PERF_MEM_S(a, s) \
> > + (((u64)PERF_MEM_##a##_##s) << PERF_MEM_##a##_SHIFT)
> > +
>
> Would be nice to get feedback from PowerPC folks to see how well
> this matches their memory profiling hw capabilities?
>
> I suspect there's a lot of differences, but one can always hope
> ...
>
> If there's some hope for unification we could at least shape it
> in a way that they could pick up and extend.

Thanks for Ccing.

While on the topic of sampled instructions, POWER saves following information
(in addition to the above memory info) for sampled instructions.

- whether the sampled instruction encountered a stall
- the reasons for the stall.
- whether the instruction was from hypervisor
- there was a branch mis-predict,
- thresholding information

These are clubbed into an "event vector" that is saved for sampled
instructions. We have been meaning to find ways to present that to
to user space. Are there plans to retreive and present these too.

Sukadev



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