| Message ID | 8760i16lxj.fsf@concordia.ellerman.id.au (mailing list archive) |
|---|---|
| State | Not Applicable |
| Headers | show |
On Wednesday 19 April 2017 10:20 AM, Michael Ellerman wrote: > Peter Zijlstra <peterz@infradead.org> writes: > >> On Tue, Apr 11, 2017 at 07:21:05AM +0530, Madhavan Srinivasan wrote: >>> From: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com> >>> >>> perf_mem_data_src is an union that is initialized via the ->val field >>> and accessed via the bitmap fields. For this to work on big endian >>> platforms (Which is broken now), we also need a big-endian represenation >>> of perf_mem_data_src. i.e, in a big endian system, if user request >>> PERF_SAMPLE_DATA_SRC (perf report -d), will get the default value from >>> perf_sample_data_init(), which is PERF_MEM_NA. Value for PERF_MEM_NA >>> is constructed using shifts: >>> >>> /* TLB access */ >>> #define PERF_MEM_TLB_NA 0x01 /* not available */ >>> ... >>> #define PERF_MEM_TLB_SHIFT 26 >>> >>> #define PERF_MEM_S(a, s) \ >>> (((__u64)PERF_MEM_##a##_##s) << PERF_MEM_##a##_SHIFT) >>> >>> #define PERF_MEM_NA (PERF_MEM_S(OP, NA) |\ >>> PERF_MEM_S(LVL, NA) |\ >>> PERF_MEM_S(SNOOP, NA) |\ >>> PERF_MEM_S(LOCK, NA) |\ >>> PERF_MEM_S(TLB, NA)) >>> >>> Which works out as: >>> >>> ((0x01 << 0) | (0x01 << 5) | (0x01 << 19) | (0x01 << 24) | (0x01 << 26)) >>> >>> Which means the PERF_MEM_NA value comes out of the kernel as 0x5080021 >>> in CPU endian. >>> >>> But then in the perf tool, the code uses the bitfields to inspect the >>> value, and currently the bitfields are defined using little endian >>> ordering. >>> >>> So eg. in perf_mem__tlb_scnprintf() we see: >>> data_src->val = 0x5080021 >>> op = 0x0 >>> lvl = 0x0 >>> snoop = 0x0 >>> lock = 0x0 >>> dtlb = 0x0 >>> rsvd = 0x5080021 >>> >>> Patch does a minimal fix of adding big endian definition of the bitfields >>> to match the values that are already exported by the kernel on big endian. >>> And it makes no change on little endian. >> I think it is important to note that there are no current big-endian >> users. So 'fixing' this will not break anybody and will ensure future >> users (next patch) will work correctly. > Actually that's only partly true. As I describe above the PERF_MEM_NA > value is currently exported on BE platforms when a user requests it. > > So I added this text after the output from perf_mem__tlb_scnprintf(): > > Because of the way the perf tool code is written this is still displayed to the > user as "N/A", so there is no bug visible at the UI level. > > Currently there are no big endian architectures which export a meaningful > value (ie. other than PERF_MEM_NA), so the extent of the bug on big endian > platforms is that the PERF_MEM_NA value is exported incorrectly as described > above. Subsequent patches will add support on big endian powerpc for populating > the data source value. > > > Hope that is clear. > > It also occurred to me that we don't actually have to redefine the whole > union, it's only the bitfields that matter, so we could reduce the diff > to: > > diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h > index c66a485a24ac..97152c79df6b 100644 > --- a/include/uapi/linux/perf_event.h > +++ b/include/uapi/linux/perf_event.h > @@ -894,12 +894,23 @@ enum perf_callchain_context { > union perf_mem_data_src { > __u64 val; > struct { > +#if defined(__LITTLE_ENDIAN_BITFIELD) > __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; > +#elif defined(__BIG_ENDIAN_BITFIELD) > + __u64 mem_rsvd:31, > + mem_dtlb:7, /* tlb access */ > + mem_lock:2, /* lock instr */ > + mem_snoop:5, /* snoop mode */ > + mem_lvl:14, /* memory hierarchy level */ > + mem_op:5; /* type of opcode */ > +#else > +#error "Unknown endianness" > +#endif > }; > }; > > > That looks better to me, thoughts? Yep. Looks fine to me and also tested the same. Maddy > > cheers >
Madhavan Srinivasan <maddy@linux.vnet.ibm.com> writes: > On Wednesday 19 April 2017 10:20 AM, Michael Ellerman wrote: >> It also occurred to me that we don't actually have to redefine the whole >> union, it's only the bitfields that matter, so we could reduce the diff >> to: >> >> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h >> index c66a485a24ac..97152c79df6b 100644 >> --- a/include/uapi/linux/perf_event.h >> +++ b/include/uapi/linux/perf_event.h >> @@ -894,12 +894,23 @@ enum perf_callchain_context { >> union perf_mem_data_src { >> __u64 val; >> struct { >> +#if defined(__LITTLE_ENDIAN_BITFIELD) >> __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; >> +#elif defined(__BIG_ENDIAN_BITFIELD) >> + __u64 mem_rsvd:31, >> + mem_dtlb:7, /* tlb access */ >> + mem_lock:2, /* lock instr */ >> + mem_snoop:5, /* snoop mode */ >> + mem_lvl:14, /* memory hierarchy level */ >> + mem_op:5; /* type of opcode */ >> +#else >> +#error "Unknown endianness" >> +#endif >> }; >> }; >> >> >> That looks better to me, thoughts? > > Yep. Looks fine to me and also tested the same. I merged the original version, as that's what Peterz acked and I didn't want to block the series any longer. I'll send an incremental patch to do the cleanup. cheers
diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h index c66a485a24ac..97152c79df6b 100644 --- a/include/uapi/linux/perf_event.h +++ b/include/uapi/linux/perf_event.h @@ -894,12 +894,23 @@ enum perf_callchain_context { union perf_mem_data_src { __u64 val; struct { +#if defined(__LITTLE_ENDIAN_BITFIELD) __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; +#elif defined(__BIG_ENDIAN_BITFIELD) + __u64 mem_rsvd:31, + mem_dtlb:7, /* tlb access */ + mem_lock:2, /* lock instr */ + mem_snoop:5, /* snoop mode */ + mem_lvl:14, /* memory hierarchy level */ + mem_op:5; /* type of opcode */ +#else +#error "Unknown endianness" +#endif }; };