Messages in this thread | | | Date | Wed, 30 Nov 2022 16:56:32 +0000 | Subject | Re: [PATCH V5 6/7] arm64/perf: Add BRBE driver | From | James Clark <> |
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On 30/11/2022 04:49, Anshuman Khandual wrote: > > > On 11/29/22 21:23, James Clark wrote: >> >> >> On 07/11/2022 06:25, Anshuman Khandual wrote: >>> This adds a BRBE driver which implements all the required helper functions >>> for struct arm_pmu. Following functions are defined by this driver which >>> will configure, enable, capture, reset and disable BRBE buffer HW as and >>> when requested via perf branch stack sampling framework. >> >> Hi Anshuman, >> >> I've got a rough version of an updated test for branch stacks here [1]. >> A couple of interesting things that I've noticed running it: >> >> First one is that sometimes I get (null) for the branch type. Debugging >> in GDB shows me that the type is actually type == PERF_BR_EXTEND_ABI && >> new_type == 11. I can't see how this is possible looking at the driver > > Hmm, that is strange. > > brbe_fetch_perf_type() evaluates captured brbinf and extracts BRBE branch > type and later maps into perf branch types. All new perf branch types are > contained inside [PERF_BR_NEW_FAULT_ALGN = 0 .. PERF_BR_NEW_ARCH_5 = 7]. > Hence wondering how '11' can be a new_type value after PERF_BR_EXTEND_ABI > switch.
I got to the bottom of the issue and posted the fix here [2]. A new entry was added to the branch records somewhere around the time new_type was added and it wasn't added to Perf so the records weren't being interpreted properly.
> >> code. I think I saw this on a previous version of the patchset too but >> didn't mention it because I thought it wasn't significant, but now I see >> that something strange is going on. An interesting pattern is that they >> are always after ERET samples and go from userspace to kernel: > > Unless it can be ascertained that wrong values are getting passed into the > perf ring buffer via cpuc->branches->brbe_entries[idx].[type | new_type], > the problem might be with perf report parsing the branch records ? > > There are valid new branch types such as ARM64_DEBUG_DATA reported after > ERET records as well. I guess the only way to figure out the problem here > is to track the errant branch record from cpuc->branches->brbe_entries to > all the way upto perf report processing. > >> >> 41992866945460 0x6e8 [0x360]: PERF_RECORD_SAMPLE(IP, 0x1): 501/501: >> 0xffff800008010118 period: 1229 addr: 0 >> ... branch stack: nr:34 >> .. 007a9988 -> 00000000 0 cycles P 9fbfbfbf IRQ >> .. 00000000 -> 007a9988 0 cycles P 9fbfbfbf ERET >> .. 007a9988 -> 00000000 0 cycles P 9fbfbfbf (null) >> .. 00747668 -> 007a9988 0 cycles P 9fbfbfbf CALL >> .. 00747664 -> 00747660 0 cycles P 9fbfbfbf COND >> .. 00747664 -> 00747660 0 cycles P 9fbfbfbf COND >> .. 00747664 -> 00747660 0 cycles P 9fbfbfbf COND >> .. 00747664 -> 00747660 0 cycles P 9fbfbfbf COND >> .. 00747664 -> 00747660 0 cycles P 9fbfbfbf COND >> .. 00747664 -> 00747660 0 cycles P 9fbfbfbf COND >> .. 00747664 -> 00747660 0 cycles P 9fbfbfbf COND >> .. 00747664 -> 00747660 0 cycles P 9fbfbfbf COND >> .. 00747664 -> 00747660 0 cycles P 9fbfbfbf COND >> .. 00747664 -> 00747660 0 cycles P 9fbfbfbf COND >> .. 00747664 -> 00747660 0 cycles P 9fbfbfbf COND >> .. 00747664 -> 00747660 0 cycles P 9fbfbfbf COND >> .. 00747664 -> 00747660 0 cycles P 9fbfbfbf COND >> .. 00747664 -> 00747660 0 cycles P 9fbfbfbf COND >> .. 00747664 -> 00747660 0 cycles P 9fbfbfbf COND >> .. 00747664 -> 00747660 0 cycles P 9fbfbfbf COND >> .. 00747664 -> 00747660 0 cycles P 9fbfbfbf COND >> .. 00000000 -> 00747658 0 cycles P 9fbfbfbf ERET >> .. 00747658 -> 00000000 0 cycles P 9fbfbfbf ARM64_DEBUG_DATA >> .. 00000000 -> 00747650 0 cycles P 9fbfbfbf ERET >> .. 00747650 -> 00000000 0 cycles P 9fbfbfbf ARM64_DEBUG_DATA >> .. 00747624 -> 00747634 0 cycles P 9fbfbfbf COND >> .. 00000000 -> 007475f4 0 cycles P 9fbfbfbf ERET >> .. 007475f4 -> 00000000 0 cycles P 9fbfbfbf ARM64_DEBUG_DATA >> .. 00000000 -> 007475e8 0 cycles P 9fbfbfbf ERET >> .. 007475e8 -> 00000000 0 cycles P 9fbfbfbf (null) >> .. 004005ac -> 007475e8 0 cycles P 9fbfbfbf CALL >> .. 00000000 -> 00400564 0 cycles P 9fbfbfbf ERET >> .. 00400564 -> 00000000 0 cycles P 9fbfbfbf (null) >> .. 00000000 -> 00400564 0 cycles P 9fbfbfbf ERET >> .. thread: perf:501 >> ...... dso: [kernel.kallsyms] >> >> The second one is that sometimes I get kernel addresses and RET branches >> even if the option is any_call,u. The pattern here is that it's the last >> non empty branch stack of a run, so maybe there is some disable path >> where the filters aren't configured properly: > > The latest code (not posted), disables TRBE completely while reading the > branch records during PMU interrupt. Could you please apply those changes > as well, or rather just use the branch instead. > > https://gitlab.arm.com/linux-arm/linux-anshuman/-/commit/ab17879711f0e61c280ed52400ccde172b67e04a >
I don't think I've seen it on that version, but I need to run it a bit more to be sure.
> >> >> >> [1]: >> https://gitlab.arm.com/linux-arm/linux-jc/-/commit/7260b7bef06ac161eac88d05266e8c5c303d9881
[2]: https://lore.kernel.org/linux-perf-users/20221130165158.517385-1-james.clark@arm.com/T/#u
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