Messages in this thread | | | Subject | Re: [PATCH v4 1/6] perf arm-spe: Remove unused enum value ARM_SPE_PER_CPU_MMAPS | From | James Clark <> | Date | Thu, 15 Apr 2021 17:49:45 +0300 |
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On 15/04/2021 17:41, Leo Yan wrote: > Hi James, > > On Thu, Apr 15, 2021 at 05:13:36PM +0300, James Clark wrote: >> On 12/04/2021 12:10, Leo Yan wrote: >>> The enum value 'ARM_SPE_PER_CPU_MMAPS' is never used so remove it. >> >> Hi Leo, >> >> I think this causes an error when attempting to open a newly recorded file >> with an old version of perf. The value ARM_SPE_AUXTRACE_PRIV_MAX is used here: >> >> size_t min_sz = sizeof(u64) * ARM_SPE_AUXTRACE_PRIV_MAX; >> struct perf_record_time_conv *tc = &session->time_conv; >> struct arm_spe *spe; >> int err; >> >> if (auxtrace_info->header.size < sizeof(struct perf_record_auxtrace_info) + >> min_sz) >> return -EINVAL; >> >> And removing ARM_SPE_PER_CPU_MMAPS changes the value of ARM_SPE_AUXTRACE_PRIV_MAX. >> >> At least I think that's what's causing the problem. I get this error: >> >> ./perf report -i per-thread-spe-time.data >> 0x1c0 [0x18]: failed to process type: 70 [Invalid argument] >> Error: >> failed to process sample >> # To display the perf.data header info, please use --header/--header-only options. >> # > > Yes, when working on this patch I had concern as well. > > I carefully thought that the perf tool should be backwards-compatible, > but there have no requirement for forwards-compatibility. This is the > main reason why I kept this patch. > > If you or anyone could confirm the forwards-compatibility is required, > it's quite fine for me to drop this patch. >
Personally, I can easily imagine sending a file to someone to open with an older version and it causing friction where it could be easily avoided. And it even made testing a bit more difficult because I wanted to compare opening the same file with the patched and un-patched version. But if there is no hard requirement I can't really put too much pressure to not remove it.
> Thanks a lot for the reviewing and testing! > Leo >
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