Re: [PATCH 2/3] perf_counter: allow arch to supply event misc flags and instruction pointer

Peter Zijlstra
2009-05-14T06:45:56Z

On Thu, 2009-05-14 at 13:29 +1000, Paul Mackerras wrote:
> At present the values we put in overflow events for the misc flags
> indicating processor mode and the instruction pointer are obtained
> using the standard user_mode() and instruction_pointer() functions.
> Those functions tell you where the performance monitor interrupt
> was taken, which might not be exactly where the counter overflow
> occurred, for example because interrupts were disabled at the point
> where the overflow occurred, or because the processor had many
> instructions in flight and chose to complete some more instructions
> beyond the one that caused the counter overflow.
>
> Some architectures (e.g. powerpc) can supply more precise information
> about where the counter overflow occurred and the processor mode at
> that point. This introduces new functions, perf_misc_flags() and
> perf_instruction_pointer(), which arch code can override to provide
> more precise information if available. They have default implementations
> which are identical to the existing code.
>
> This also adds a new misc flag value, PERF_EVENT_MISC_HYPERVISOR, for
> the case where a counter overflow occurred in the hypervisor.
>
> Signed-off-by: Paul Mackerras <paulus@samba.org>
> ---
> include/linux/perf_counter.h | 7 +++++++
> kernel/perf_counter.c | 5 ++---
> 2 files changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h
> index 614f921..2b12d98 100644
> --- a/include/linux/perf_counter.h
> +++ b/include/linux/perf_counter.h
> @@ -213,6 +213,7 @@ struct perf_counter_mmap_page {
> #define PERF_EVENT_MISC_KERNEL (1 << 0)
> #define PERF_EVENT_MISC_USER (1 << 1)
> #define PERF_EVENT_MISC_OVERFLOW (1 << 2)
> +#define PERF_EVENT_MISC_HYPERVISOR (1 << 3)

Ah, I think I've taught userspace that either !USER && !KERNEL or USER
&& KERNEL is HV information, since neither really makes sense :-)

> struct perf_event_header {
> __u32 type;
> @@ -588,6 +589,12 @@ extern int sysctl_perf_counter_mlock;
>
> extern void perf_counter_init(void);
>
> +#ifndef perf_misc_flags
> +#define perf_misc_flags(regs) (user_mode(regs) ? PERF_EVENT_MISC_USER : \
> + PERF_EVENT_MISC_KERNEL)
> +#define perf_instruction_pointer(regs) instruction_pointer(regs)
> +#endif
> +
> #else
> static inline void
> perf_counter_task_sched_in(struct task_struct *task, int cpu) { }
> diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
> index ff166c1..89568de 100644
> --- a/kernel/perf_counter.c
> +++ b/kernel/perf_counter.c
> @@ -1978,11 +1978,10 @@ static void perf_counter_output(struct perf_counter *counter,
> header.size = sizeof(header);
>
> header.misc = PERF_EVENT_MISC_OVERFLOW;
> - header.misc |= user_mode(regs) ?
> - PERF_EVENT_MISC_USER : PERF_EVENT_MISC_KERNEL;
> + header.misc |= perf_misc_flags(regs);
>
> if (record_type & PERF_RECORD_IP) {
> - ip = instruction_pointer(regs);
> + ip = perf_instruction_pointer(regs);
> header.type |= PERF_RECORD_IP;
> header.size += sizeof(ip);
> }