Messages in this thread | | | Date | Thu, 13 Apr 2017 14:38:49 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH v3 1/6] powerpc/perf: Define big-endian version of perf_mem_data_src |
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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.
Aside from that amendment,
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
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