Messages in this thread | ![/](/images/icornerl.gif) | | Date | Mon, 3 Jun 2024 14:48:58 +0530 | Subject | Re: [PATCH V17 0/9] arm64/perf: Enable branch stack sampling | From | Anshuman Khandual <> |
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On 5/30/24 15:33, James Clark wrote: > > > On 05/04/2024 03:46, Anshuman Khandual wrote: >> This series enables perf branch stack sampling support on arm64 platform >> via a new arch feature called Branch Record Buffer Extension (BRBE). All >> the relevant register definitions could be accessed here. >> >> https://developer.arm.com/documentation/ddi0601/2021-12/AArch64-Registers >> >> This series applies on 6.9-rc2. >> >> Also this series is being hosted below for quick access, review and test. >> >> https://git.gitlab.arm.com/linux-arm/linux-anshuman.git (brbe_v17) >> >> There are still some open questions regarding handling multiple perf events >> with different privilege branch filters getting on the same PMU, supporting >> guest branch stack tracing from the host etc. Finally also looking for some >> suggestions regarding supporting BRBE inside the guest. The series has been >> re-organized completely as suggested earlier. > > For guest support I'm still of this opinion: > > * No support for the host looking into guests (the addresses don't > make sense anyway without also running Perf record in the guest) > * Save and restore the host buffer and registers on guest switch (if > it was ever used by either host or guest) > * Let the guest do whatever it wants with BRBE without any > virtualisation > > Merging this with the current PMU virtualistion stuff seems like a lot > of work for no use case (host looking into guests). Having said that, it > might not even be worth discussing on this patchset apart from "no guest > support", and we can do it later to avoid confusion that it's being > proposed for this version.
Agreed, let's just have "no guest support" for now in this proposed series without any more additional changes to keep things simpler and separated. I will also update the cover letter next time around making this clear.
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