Messages in this thread | | | From | Michael Ellerman <> | Subject | Re: [PATCH v1 01/13] perf/core: add union to struct perf_branch_entry | Date | Sat, 11 Sep 2021 00:16:20 +1000 |
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Michael Ellerman <mpe@ellerman.id.au> writes: > Peter Zijlstra <peterz@infradead.org> writes: >> On Thu, Sep 09, 2021 at 12:56:48AM -0700, Stephane Eranian wrote: >>> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h >>> index f92880a15645..eb11f383f4be 100644 >>> --- a/include/uapi/linux/perf_event.h >>> +++ b/include/uapi/linux/perf_event.h >>> @@ -1329,13 +1329,18 @@ union perf_mem_data_src { >>> struct perf_branch_entry { >>> __u64 from; >>> __u64 to; >>> - __u64 mispred:1, /* target mispredicted */ >>> - predicted:1,/* target predicted */ >>> - in_tx:1, /* in transaction */ >>> - abort:1, /* transaction abort */ >>> - cycles:16, /* cycle count to last branch */ >>> - type:4, /* branch type */ >>> - reserved:40; >>> + union { >>> + __u64 val; /* to make it easier to clear all fields */ >>> + struct { >>> + __u64 mispred:1, /* target mispredicted */ >>> + predicted:1,/* target predicted */ >>> + in_tx:1, /* in transaction */ >>> + abort:1, /* transaction abort */ >>> + cycles:16, /* cycle count to last branch */ >>> + type:4, /* branch type */ >>> + reserved:40; >>> + }; >>> + }; >>> }; >> >> >> Hurpmh... all other bitfields have ENDIAN_BITFIELD things except this >> one. Power folks, could you please have a look? > > The bit number of each field changes between big and little endian, but > as long as kernel and userspace are the same endian, and both only > access values via the bitfields then it works. ... > > It does look like we have a bug in perf tool though, if I take a > perf.data from a big endian system to a little endian one I don't see > any of the branch flags decoded. eg: > > BE: > > 2413132652524 0x1db8 [0x2d0]: PERF_RECORD_SAMPLE(IP, 0x1): 5279/5279: 0xc00000000045c028 period: 923003 addr: 0 > ... branch stack: nr:28 > ..... 0: c00000000045c028 -> c00000000dce7604 0 cycles P 0 > > LE: > > 2413132652524 0x1db8 [0x2d0]: PERF_RECORD_SAMPLE(IP, 0x1): 5279/5279: 0xc00000000045c028 period: 923003 addr: 0 > ... branch stack: nr:28 > ..... 0: c00000000045c028 -> c00000000dce7604 0 cycles 0 > ^ > missing P > > I guess we're missing a byte swap somewhere.
Ugh. We _do_ have a byte swap, but we also need a bit swap.
That works for the single bit fields, not sure if it will for the multi-bit fields.
So that's a bit of a mess :/
cheers
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