Messages in this thread | | | Date | Wed, 18 May 2022 10:44:57 +0100 | Subject | Re: [PATCH v2 4/4] perf tools: arm64: Add support for VG register | From | James Clark <> |
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On 17/05/2022 14:19, Leo Yan wrote: > On Tue, May 17, 2022 at 11:20:05AM +0100, James Clark wrote: >> Add the name of the VG register so it can be used in --user-regs >> >> The event will fail to open if the register is requested but not >> available so only add it to the mask if the kernel supports sve and also >> if it supports that specific register. >> >> Signed-off-by: James Clark <james.clark@arm.com> >> --- >> tools/perf/arch/arm64/util/perf_regs.c | 34 ++++++++++++++++++++++++++ >> tools/perf/util/perf_regs.c | 2 ++ >> 2 files changed, 36 insertions(+) >> >> diff --git a/tools/perf/arch/arm64/util/perf_regs.c b/tools/perf/arch/arm64/util/perf_regs.c >> index 476b037eea1c..c0a921512a90 100644 >> --- a/tools/perf/arch/arm64/util/perf_regs.c >> +++ b/tools/perf/arch/arm64/util/perf_regs.c >> @@ -2,9 +2,11 @@ >> #include <errno.h> >> #include <regex.h> >> #include <string.h> >> +#include <sys/auxv.h> >> #include <linux/kernel.h> >> #include <linux/zalloc.h> >> >> +#include "../../../perf-sys.h" >> #include "../../../util/debug.h" >> #include "../../../util/event.h" >> #include "../../../util/perf_regs.h" >> @@ -43,6 +45,7 @@ const struct sample_reg sample_reg_masks[] = { >> SMPL_REG(lr, PERF_REG_ARM64_LR), >> SMPL_REG(sp, PERF_REG_ARM64_SP), >> SMPL_REG(pc, PERF_REG_ARM64_PC), >> + SMPL_REG(vg, PERF_REG_ARM64_VG), >> SMPL_REG_END >> }; >> >> @@ -131,3 +134,34 @@ int arch_sdt_arg_parse_op(char *old_op, char **new_op) >> >> return SDT_ARG_VALID; >> } >> + >> +uint64_t arch__user_reg_mask(void) >> +{ >> + struct perf_event_attr attr = { >> + .type = PERF_TYPE_HARDWARE, >> + .config = PERF_COUNT_HW_CPU_CYCLES, >> + .sample_type = PERF_SAMPLE_REGS_USER, >> + .disabled = 1, >> + .exclude_kernel = 1, >> + .sample_period = 1, >> + .sample_regs_user = PERF_REGS_MASK >> + }; >> + int fd; >> + >> + if (getauxval(AT_HWCAP) & HWCAP_SVE) >> + attr.sample_regs_user |= SMPL_REG_MASK(PERF_REG_ARM64_VG); >> + >> + /* >> + * Check if the pmu supports perf extended regs, before >> + * returning the register mask to sample. >> + */ >> + if (attr.sample_regs_user != PERF_REGS_MASK) { >> + event_attr_init(&attr); >> + fd = sys_perf_event_open(&attr, 0, -1, -1, 0); >> + if (fd != -1) { >> + close(fd); >> + return attr.sample_regs_user; >> + } >> + } > > Just curious, since we can know SVE is supported from reading > auxiliary value, can we directly return the register mask as below? > > PERF_REGS_MASK | SMPL_REG_MASK(PERF_REG_ARM64_VG);
I was trying to cover the case where the system supports SVE, but the kernel doesn't have my changes to add the VG register yet.
Technically I could just attempt to open the event without checking for SVE first and see if it works or not. But I preferred to be explicit so it's obvious why we're doing that.
James
> > Except this question, this patch looks good to me. > > Thanks, > Leo > >> + return PERF_REGS_MASK; >> +} >> diff --git a/tools/perf/util/perf_regs.c b/tools/perf/util/perf_regs.c >> index a982e40ee5a9..872dd3d38782 100644 >> --- a/tools/perf/util/perf_regs.c >> +++ b/tools/perf/util/perf_regs.c >> @@ -103,6 +103,8 @@ static const char *__perf_reg_name_arm64(int id) >> return "lr"; >> case PERF_REG_ARM64_PC: >> return "pc"; >> + case PERF_REG_ARM64_VG: >> + return "vg"; >> default: >> return NULL; >> } >> -- >> 2.28.0 >>
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