Re: [9front] time v2

Re: [9front] time v2

[Alex Musolino]

What's the point of the segattach?  Can you not just add RFMEM to the
rfork flags?

Also, you probably ought to be setting t0 again before the second call
to exec.

Re: [9front] time v4

[BurnZeZ]

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On Sun Aug 12 05:40:12 GMT 2018, alex@musolino.id.au wrote:
> What's the point of the segattach?  Can you not just add RFMEM to the
> rfork flags?
char	output[4096];
output would be shared, and the child process uses it for the exec
path stuff.
I thought about using RFMEM at first, but it ended up being simpler
this way.

> Also, you probably ought to be setting t0 again before the second call
> to exec.
You would miss out on accounting for 9p latency for the first exec()
attempt, but I think you’re right, since the fact that t0 is set
after the fork() indicates we’re not worried about absolute time
from the parent process’ perspective.

Attached diff contains that change.

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diff -r 5c5acc9ab7a5 sys/src/cmd/time.c
--- a/sys/src/cmd/time.c	Sat Aug 11 16:19:32 2018 +0200
+++ b/sys/src/cmd/time.c	Sun Aug 12 18:17:11 2018 +0000
@@ -14,20 +14,27 @@
 	long l;
 	char *p;
 	char err[ERRMAX];
+	vlong *t0, t1;
+	enum { SEC = 1000000000ULL };
 
 	if(argc <= 1){
 		fprint(2, "usage: time command\n");
 		exits("usage");
 	}
 
+	if((t0 = segattach(SG_CEXEC, "shared", nil, sizeof(*t0))) == (void*)-1)
+		sysfatal("segattach: %r");
+	*t0 = 0;
 	switch(fork()){
 	case -1:
 		error("fork");
 	case 0:
+		*t0 = nsec();
 		exec(argv[1], &argv[1]);
 		if(argv[1][0] != '/' && strncmp(argv[1], "./", 2) &&
 		   strncmp(argv[1], "../", 3)){
 			sprint(output, "/bin/%s", argv[1]);
+			*t0 = nsec();
 			exec(output, &argv[1]);
 		}
 		error(argv[1]);
@@ -43,12 +50,14 @@
 			goto loop;
 		error("wait");
 	}
+	t1 = nsec();
 	l = w->time[0];
 	add("%ld.%.2ldu", l/1000, (l%1000)/10);
 	l = w->time[1];
 	add("%ld.%.2lds", l/1000, (l%1000)/10);
 	l = w->time[2];
 	add("%ld.%.2ldr", l/1000, (l%1000)/10);
+	add("%lld.%.9lldt", (t1-*t0)/SEC, (t1-*t0)%SEC);
 	add("\t");
 	for(i=1; i<argc; i++){
 		add("%s", argv[i], 0);