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

[Pawel Moll <pawel.moll@arm.com>]

On Wed, 2013-02-06 at 01:19 +0000, Steven Rostedt wrote:
> If people are worried about adding a bunch of new perf syscalls, maybe
> add a sys_perf_control() system call that works like an ioctl but
> without a file descriptor. Something for things that don't require an
> event attached to it, like to retrieve a time stamp counter that perf
> uses, but done in a way that it could be used for other things perf
> related that does not require an event.

Something along these lines? (completely untested and of course missing
all the #defines __NR_perf_control xxx)

8<-----------------
diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index 4f63c05..be7409b 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -322,6 +322,11 @@ enum perf_event_ioc_flags {
 };
 
 /*
+ * Command codes for ioctl-like sys_perf_control interface:
+ */
+#define PERF_CONTROL_GET_TIME		_IOR('$', 0, __u64)
+
+/*
  * Structure of the page that can be mapped via mmap
  */
 struct perf_event_mmap_page {
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 301079d..750404d 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6678,6 +6678,29 @@ err_fd:
 }
 
 /**
+ * sys_perf_control - ioctl-like interface to control system-wide
+ *		      perf behaviour
+ *
+ * @cmd:	one of the PERF_CONTROL_* commands
+ * @arg:	command-specific argument
+ */
+SYSCALL_DEFINE2(perf_control, unsigned int, cmd, unsigned long, arg)
+{
+	switch (cmd) {
+	case PERF_CONTROL_GET_TIME:
+	{
+		u64 time = perf_clock();
+		if (copy_to_user((void __user *)arg, &time, sizeof(time)))
+			return -EFAULT;
+		return 0;
+	}
+
+	default:
+		return -ENOTTY;
+	}
+}
+
+/**
  * perf_event_create_kernel_counter
  *
  * @attr: attributes of the counter to create
8<-----------------

Cheers!

Pawel