Messages in this thread | | | From | Anshuman Khandual <> | Subject | Re: [PATCH 1/2] perf: Add more generic branch types | Date | Fri, 4 Feb 2022 10:26:54 +0530 |
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On 2/2/22 5:28 PM, Mark Rutland wrote: > Hi Anshuman, > > On Fri, Jan 28, 2022 at 11:14:12AM +0530, Anshuman Khandual wrote: >> This expands generic branch type classification by adding some more entries >> , that can still be represented with the existing 4 bit 'type' field. While
^ >> here this also updates the x86 implementation with these new branch types. > > It looks like there's some whitespace damage here.
Are you referring the above ? I will have a look.
> >>From a quick scan of the below, I think the "exception return" and "IRQ > exception" types are somewhat generic, and could be added now (aside from any > bikeshedding over names), but: > > * For IRQ vs FIQ, we might just want to have a top-level "asynchronous > exception" type, and then further divide that with a separate field. That way > it's easier to extend in future if new exceptions are added.
Okay. But that might lead to a hierarchical bit fields design where as the current one is just linear.
> > * I don't think the debug state entry/exits make sense as generic branch types,
From BRBE perspective, a branch is any control flow change including exception level change, debug enter, debug exit etc. If exception and its return can be classified as 'branches' why not debug state change ? Are there no similar debug states transition on other platforms ?
> since those are somewhat specific to the ARM architecutre, and it might make > sense to define generic PERF_BR_ARCH* definitions instead.
Makes sense but corresponding bit field layout change in branch_sample_type will remain a challenge.
> > * Given the next patch extends the field, and therei are potential ABI problems > with that, we might need to reserve a value for ABI extensibility purposes, > and I suspect we need to do that *first*. More comments on the subsequent > patch.
Sure, understood.
> >> Cc: Peter Zijlstra <peterz@infradead.org> >> Cc: Ingo Molnar <mingo@redhat.com> >> Cc: Arnaldo Carvalho de Melo <acme@kernel.org> >> Cc: Mark Rutland <mark.rutland@arm.com> >> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com> >> Cc: Jiri Olsa <jolsa@redhat.com> >> Cc: Namhyung Kim <namhyung@kernel.org> >> Cc: Will Deacon <will@kernel.org> >> Cc: linux-arm-kernel@lists.infradead.org >> Cc: linux-perf-users@vger.kernel.org >> Cc: linux-kernel@vger.kernel.org >> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com> >> --- >> arch/x86/events/intel/lbr.c | 4 ++-- >> include/uapi/linux/perf_event.h | 5 +++++ >> tools/include/uapi/linux/perf_event.h | 5 +++++ >> tools/perf/util/branch.c | 7 ++++++- >> 4 files changed, 18 insertions(+), 3 deletions(-) >> >> diff --git a/arch/x86/events/intel/lbr.c b/arch/x86/events/intel/lbr.c >> index 8043213b75a5..9f86fac8c6a5 100644 >> --- a/arch/x86/events/intel/lbr.c >> +++ b/arch/x86/events/intel/lbr.c >> @@ -1336,10 +1336,10 @@ static int branch_map[X86_BR_TYPE_MAP_MAX] = { >> PERF_BR_SYSCALL, /* X86_BR_SYSCALL */ >> PERF_BR_SYSRET, /* X86_BR_SYSRET */ >> PERF_BR_UNKNOWN, /* X86_BR_INT */ >> - PERF_BR_UNKNOWN, /* X86_BR_IRET */ >> + PERF_BR_EXPT_RET, /* X86_BR_IRET */ >> PERF_BR_COND, /* X86_BR_JCC */ >> PERF_BR_UNCOND, /* X86_BR_JMP */ >> - PERF_BR_UNKNOWN, /* X86_BR_IRQ */ >> + PERF_BR_IRQ, /* X86_BR_IRQ */ >> PERF_BR_IND_CALL, /* X86_BR_IND_CALL */ >> PERF_BR_UNKNOWN, /* X86_BR_ABORT */ >> PERF_BR_UNKNOWN, /* X86_BR_IN_TX */ > > This presumably changes the values reported to userspace, so the commit message > should mention that and explain why that is not a problem.
Okay.
> >> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h >> index 1b65042ab1db..b91d0f575d0c 100644 >> --- a/include/uapi/linux/perf_event.h >> +++ b/include/uapi/linux/perf_event.h >> @@ -251,6 +251,11 @@ enum { >> PERF_BR_SYSRET = 8, /* syscall return */ >> PERF_BR_COND_CALL = 9, /* conditional function call */ >> PERF_BR_COND_RET = 10, /* conditional function return */ >> + PERF_BR_EXPT_RET = 11, /* exception return */ > > We don't use 'EXPT' anywhere else, so it might be better to just use 'ERET'. > IIUC that's the naming the x86 FRED stuff is going to use anyhow.
Sure, will change.
> >> + PERF_BR_IRQ = 12, /* irq */ > > This looks somewhat generic, so adding it now makes sense to me, but ... > >> + PERF_BR_FIQ = 13, /* fiq */ > > ... this is arguably just a idfferent class of interrupt from the PoV of Linux, > and the naming is ARM-specific, so I don't think this makes sense to add *now*.
I assume 'now' --> without ABI extension.
> As above, maybe it would be better to have a generic "aynchronous exception" or > "interrupt" type, and a separate field to distinguish specific types of those. > >> + PERF_BR_DEBUG_HALT = 14, /* debug halt */ >> + PERF_BR_DEBUG_EXIT = 15, /* debug exit */ > > For the benefit of those not familiar with the ARM architecture, "debug halt" > and "debug exit" usually refer to "debug state", which is what an external > (e.g. JTAG) debugger uses rather than the usual self-hosted debug stuff that > Linux uses. > > Given that, I'm not sure these are very generic, and I suspect it would be > better to have more generic PERF_BR_ARCH_* entries for things like this.
Sure, will try and come up with something similar.
> > Thanks, > Mark. > >> PERF_BR_MAX, >> }; >> >> diff --git a/tools/include/uapi/linux/perf_event.h b/tools/include/uapi/linux/perf_event.h >> index 4cd39aaccbe7..1882054e8684 100644 >> --- a/tools/include/uapi/linux/perf_event.h >> +++ b/tools/include/uapi/linux/perf_event.h >> @@ -251,6 +251,11 @@ enum { >> PERF_BR_SYSRET = 8, /* syscall return */ >> PERF_BR_COND_CALL = 9, /* conditional function call */ >> PERF_BR_COND_RET = 10, /* conditional function return */ >> + PERF_BR_EXPT_RET = 11, /* exception return */ >> + PERF_BR_IRQ = 12, /* irq */ >> + PERF_BR_FIQ = 13, /* fiq */ >> + PERF_BR_DEBUG_HALT = 14, /* debug halt */ >> + PERF_BR_DEBUG_EXIT = 15, /* debug exit */ >> PERF_BR_MAX, >> }; >> >> diff --git a/tools/perf/util/branch.c b/tools/perf/util/branch.c >> index 2285b1eb3128..74e5e67b1779 100644 >> --- a/tools/perf/util/branch.c >> +++ b/tools/perf/util/branch.c >> @@ -49,7 +49,12 @@ const char *branch_type_name(int type) >> "SYSCALL", >> "SYSRET", >> "COND_CALL", >> - "COND_RET" >> + "COND_RET", >> + "EXPT_RET", >> + "IRQ", >> + "FIQ", >> + "DEBUG_HALT", >> + "DEBUG_EXIT" >> }; >> >> if (type >= 0 && type < PERF_BR_MAX) >> -- >> 2.25.1 >>
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