Re: [RFC] perf: need to expose sched_clock to correlate user samples with kernel samples

From: David Ahern <dsahern@gmail.com>
To: Pawel Moll <pawel.moll@arm.com>,
	Peter Zijlstra <peterz@infradead.org>,
	"mingo@elte.hu" <mingo@elte.hu>
Cc: Stephane Eranian <eranian@google.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Paul Mackerras <paulus@samba.org>,
	Anton Blanchard <anton@samba.org>,
	Will Deacon <Will.Deacon@arm.com>,
	"ak@linux.intel.com" <ak@linux.intel.com>,
	Pekka Enberg <penberg@gmail.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Robert Richter <robert.richter@amd.com>,
	tglx <tglx@linutronix.de>, John Stultz <john.stultz@linaro.org>
Subject: Re: [RFC] perf: need to expose sched_clock to correlate user samples with kernel samples
Date: Tue, 05 Feb 2013 14:18:41 -0700	[thread overview]
Message-ID: <51117731.4010105@gmail.com> (raw)
In-Reply-To: <1359728280.8360.15.camel@hornet>

On 2/1/13 7:18 AM, Pawel Moll wrote:
> 8<---
>  From 2ad51a27fbf64bf98cee190efc3fbd7002819692 Mon Sep 17 00:00:00 2001
> From: Pawel Moll <pawel.moll@arm.com>
> Date: Fri, 1 Feb 2013 14:03:56 +0000
> Subject: [PATCH] perf: Add ioctl to return current time value
>
> To co-relate user space events with the perf events stream
> a current (as in: "what time(stamp) is it now?") time value
> must be made available.
>
> This patch adds a perf ioctl that makes this possible.

Are there any objections to this approach? I need a solution for my 
time-of-day patch as well.

David

>
> Signed-off-by: Pawel Moll <pawel.moll@arm.com>
> ---
>   include/uapi/linux/perf_event.h |    1 +
>   kernel/events/core.c            |    8 ++++++++
>   2 files changed, 9 insertions(+)
>
> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> index 4f63c05..b745fb0 100644
> --- a/include/uapi/linux/perf_event.h
> +++ b/include/uapi/linux/perf_event.h
> @@ -316,6 +316,7 @@ struct perf_event_attr {
>   #define PERF_EVENT_IOC_PERIOD		_IOW('$', 4, __u64)
>   #define PERF_EVENT_IOC_SET_OUTPUT	_IO ('$', 5)
>   #define PERF_EVENT_IOC_SET_FILTER	_IOW('$', 6, char *)
> +#define PERF_EVENT_IOC_GET_TIME		_IOR('$', 7, __u64)
>
>   enum perf_event_ioc_flags {
>   	PERF_IOC_FLAG_GROUP		= 1U << 0,
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 301079d..4202b1c 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -3298,6 +3298,14 @@ static long perf_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
>   	case PERF_EVENT_IOC_SET_FILTER:
>   		return perf_event_set_filter(event, (void __user *)arg);
>
> +	case PERF_EVENT_IOC_GET_TIME:
> +	{
> +		u64 time = perf_clock();
> +		if (copy_to_user((void __user *)arg, &time, sizeof(time)))
> +			return -EFAULT;
> +		return 0;
> +	}
> +
>   	default:
>   		return -ENOTTY;
>   	}
>