* Robert Bragg <robert@xxxxxxxxxxxxx> wrote:
> To allow for pmus that may have internal buffering (e.g. the hardware
> itself writes out data to its own circular buffer which is only
> periodically forwarded to userspace via perf) this ioctl enables
> userspace to explicitly ensure it has received all samples before a
> point in time.
>
> v2: return int error status
>
> Signed-off-by: Robert Bragg <robert@xxxxxxxxxxxxx>
> ---
> include/linux/perf_event.h | 7 +++++++
> include/uapi/linux/perf_event.h | 1 +
> kernel/events/core.c | 5 +++++
> 3 files changed, 13 insertions(+)
>
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index cf1d096..0c591eb 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -305,6 +305,13 @@ struct pmu {
> * Free pmu-private AUX data structures
> */
> void (*free_aux) (void *aux); /* optional */
> +
> + /*
> + * Flush buffered samples (E.g. for pmu hardware that writes samples to
> + * some intermediate buffer) userspace may need to explicitly ensure
> + * such samples have been forwarded to perf.
> + */
> + int (*flush) (struct perf_event *event); /*optional */
> };
>
> /**
> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> index 309211b..cbf1b80 100644
> --- a/include/uapi/linux/perf_event.h
> +++ b/include/uapi/linux/perf_event.h
> @@ -389,6 +389,7 @@ struct perf_event_attr {
> #define PERF_EVENT_IOC_SET_FILTER _IOW('$', 6, char *)
> #define PERF_EVENT_IOC_ID _IOR('$', 7, __u64 *)
> #define PERF_EVENT_IOC_SET_BPF _IOW('$', 8, __u32)
> +#define PERF_EVENT_IOC_FLUSH _IO ('$', 9)
>
> enum perf_event_ioc_flags {
> PERF_IOC_FLAG_GROUP = 1U << 0,
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 3fe532a..72daee6 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -4079,6 +4079,11 @@ static long _perf_ioctl(struct perf_event *event, unsigned int cmd, unsigned lon
> case PERF_EVENT_IOC_SET_BPF:
> return perf_event_set_bpf_prog(event, arg);
>
> + case PERF_EVENT_IOC_FLUSH:
> + if (event->pmu->flush)
> + return event->pmu->flush(event);
> + return 0;
> +
> default:
> return -ENOTTY;
> }
So 'struct file_operations' has a callback for:
int (*fsync) (struct file *, loff_t, loff_t, int datasync);
Could we use that perhaps, instead of an ioctl()? Not sure how it all
integrates with the VFS though.
Thanks,
Ingo
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