[RFC PATCH V2 2/9] perf: Extend ABI to support post-processing monotonic raw conversion

[kan . liang]

From: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>

The monotonic raw clock is not affected by NTP/PTP correction. The
calculation of the monotonic raw clock can be done in the
post-processing, which can reduce the kernel overhead.

Add hw_time in the struct perf_event_attr to tell the kernel dump the
raw HW time to user space. The perf tool will calculate the HW time
in post-processing.
Currently, only supports the monotonic raw conversion.
Only dump the raw HW time with PERF_RECORD_SAMPLE, because the accurate
HW time can only be provided in a sample by HW. For other type of
records, the user requested clock should be returned as usual. Nothing
is changed.

Add perf_event_mmap_page::cap_user_time_mono_raw ABI to dump the
conversion information. The cap_user_time_mono_raw also indicates
whether the monotonic raw conversion information is available.
If yes, the clock monotonic raw can be calculated as
mono_raw = base + ((cyc - last) * mult + nsec) >> shift

Signed-off-by: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
---
 include/uapi/linux/perf_event.h | 21 ++++++++++++++++++---
 kernel/events/core.c            |  7 +++++++
 2 files changed, 25 insertions(+), 3 deletions(-)

diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index ccb7f5dad59b..9d56fe027f6c 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -455,7 +455,8 @@ struct perf_event_attr {
 				inherit_thread :  1, /* children only inherit if cloned with CLONE_THREAD */
 				remove_on_exec :  1, /* event is removed from task on exec */
 				sigtrap        :  1, /* send synchronous SIGTRAP on event */
-				__reserved_1   : 26;
+				hw_time        :  1, /* generate raw HW time for samples */
+				__reserved_1   : 25;
 
 	union {
 		__u32		wakeup_events;	  /* wakeup every n events */
@@ -615,7 +616,8 @@ struct perf_event_mmap_page {
 				cap_user_time		: 1, /* The time_{shift,mult,offset} fields are used */
 				cap_user_time_zero	: 1, /* The time_zero field is used */
 				cap_user_time_short	: 1, /* the time_{cycle,mask} fields are used */
-				cap_____res		: 58;
+				cap_user_time_mono_raw  : 1, /* The time_mono_* fields are used */
+				cap_____res		: 57;
 		};
 	};
 
@@ -692,11 +694,24 @@ struct perf_event_mmap_page {
 	__u64	time_cycles;
 	__u64	time_mask;
 
+	/*
+	 * If cap_user_time_mono_raw, the monotonic raw clock can be calculated
+	 * from the hardware clock (e.g. TSC) 'cyc'.
+	 *
+	 * mono_raw = base + ((cyc - last) * mult + nsec) >> shift
+	 *
+	 */
+	__u64	time_mono_last;
+	__u32	time_mono_mult;
+	__u32	time_mono_shift;
+	__u64	time_mono_nsec;
+	__u64	time_mono_base;
+
 		/*
 		 * Hole for extension of the self monitor capabilities
 		 */
 
-	__u8	__reserved[116*8];	/* align to 1k. */
+	__u8	__reserved[112*8];	/* align to 1k. */
 
 	/*
 	 * Control data for the mmap() data buffer.
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 380476a934e8..f062cce2dafc 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -12135,6 +12135,13 @@ static int perf_copy_attr(struct perf_event_attr __user *uattr,
 	if (attr->sigtrap && !attr->remove_on_exec)
 		return -EINVAL;
 
+	if (attr->use_clockid) {
+		/*
+		 * Only support post-processing for the monotonic raw clock
+		 */
+		if (attr->hw_time && (attr->clockid != CLOCK_MONOTONIC_RAW))
+			return -EINVAL;
+	}
 out:
 	return ret;
 
-- 
2.35.1