Messages in this thread | | | Date | Thu, 22 Apr 2010 16:45:58 +0200 | From | Robert Richter <> | Subject | Re: [PATCH 12/12] perf, x86: implement the ibs interrupt handler |
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On 19.04.10 14:19:57, Stephane Eranian wrote: > > + perf_sample_data_init(&data, 0); > > + if (event->attr.sample_type & PERF_SAMPLE_RAW) { > > + for (i = 1; i < size; i++) > > + rdmsrl(msr++, *buf++); > > + raw.size = sizeof(u64) * size; > > + raw.data = buffer; > > + data.raw = &raw; > > + } > > + > > Need to add the padding: raw.size = sizeof(u64) * size + sizeof(u32);
The u32 size header in the raw sampling data layout leads to unaligned memory access for 64 bit values. No matter if the padding is inserted at the beginning or end of the raw sample, it introduces either on the sending or receiving side an 32 bit offset.
Wouldn't it be better to simply make size an u64 or to add another reserved u32 value to the header. This could introduce some overhead on smaller architectures, but currently this is only used on x86. The event size encoding of the ring_buffer implementation could be another alternative.
-Robert
-- Advanced Micro Devices, Inc. Operating System Research Center email: robert.richter@amd.com
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