Re: [9front] Speeding up snoopy(8)

[ori@eigenstate.org]

Quoth Lyndon Nerenberg (VE7TFX/VE6BBM) <lyndon@orthanc.ca>:
> This is coming completely out of left field, but ...
> 
> On machines that support atomic 64-bit read/write, would
> it be possible to map a single hardwired non-cacheable
> page into every process's address space and store the
> tick counter there?
> 
> --lyndon

I'm imagining something like (completely untested, just a sketch,
and almost certainly missing some places where the counters need
to be updated):

diff dfee08d50df674cd76f74320bc9c8bc6a4a95f1e uncommitted
--- a//sys/include/tos.h
+++ b//sys/include/tos.h
@@ -17,7 +17,10 @@
 	vlong	kcycles;	/* cycles spent in kernel */
 	vlong	pcycles;	/* cycles spent in process (kernel + user) */
 	ulong	pid;		/* might as well put the pid here */
-	ulong	clock;
+	ulong	clock;		/* profiling clock */
+	vlong	cycles;		/* cycles at last context switch */
+	vlong	tmono;		/* monotonic nsecs since arbitrary start time */
+	vlong	tadj;		/* timesync-adjusted nsecs since epoch */
 	/* top of stack is here */
 };
 
--- a//sys/src/libc/9sys/nsec.c
+++ b//sys/src/libc/9sys/nsec.c
@@ -24,7 +24,25 @@
 	return fd >= 0 && fd2path(fd, buf, sizeof(buf)) == 0 && strcmp(buf, name) == 0;
 }
 
+static vlong
+nsecfast()
+{
+	uvlong t;
+
+	cycles(&t);
+	return tos->tadj + (tos->cycles/tos->cyclefreq);
+}
+
 vlong
+nsecmono()
+{
+	uvlong t;
+
+	cycles(&t);
+	return tos->tmono + (tos->cycles/tos->cyclefreq);
+}
+
+vlong
 nsec(void)
 {
 	static char name[] = "/dev/bintime";
@@ -33,6 +51,8 @@
 	vlong t;
 	int f;
 
+	if(tos->cyclefreq != 0)
+		return nsecfast();
 	if(pidp != nil && *pidp == _tos->pid)
 		f = *fdp;
 	else{
--- a/sys/src/9/port/proc.c
+++ b/sys/src/9/port/proc.c
@@ -132,6 +132,8 @@
 	tos->kcycles += t - up->kentry;
 	tos->pcycles = t + up->pcycles;
 	tos->pid = up->pid;
+	tos->tmono = fastticks2ns(fastticks(nil));
+	tos->tadj = todget();
 }
 
 static void