[PATCH v7 16/16] progress: simplify performance measurement by using getnanotime()

[Karsten Blees <karsten.blees@gmail.com>]

Calculating duration from a single uint64_t is simpler than from a struct
timeval. Change throughput measurement from gettimeofday() to
getnanotime().

Also calculate misec only if needed, and change integer division to integer
multiplication + shift, which should be slightly faster.

Signed-off-by: Karsten Blees <blees@dcon.de>
---
 progress.c | 71 +++++++++++++++++++++++++++++++-------------------------------
 1 file changed, 36 insertions(+), 35 deletions(-)

diff --git a/progress.c b/progress.c
index 261314e..412e6b1 100644
--- a/progress.c
+++ b/progress.c
@@ -12,13 +12,14 @@
 #include "gettext.h"
 #include "progress.h"
 #include "strbuf.h"
+#include "trace.h"
 
 #define TP_IDX_MAX      8
 
 struct throughput {
 	off_t curr_total;
 	off_t prev_total;
-	struct timeval prev_tv;
+	uint64_t prev_ns;
 	unsigned int avg_bytes;
 	unsigned int avg_misecs;
 	unsigned int last_bytes[TP_IDX_MAX];
@@ -127,65 +128,65 @@ static void throughput_string(struct strbuf *buf, off_t total,
 void display_throughput(struct progress *progress, off_t total)
 {
 	struct throughput *tp;
-	struct timeval tv;
-	unsigned int misecs;
+	uint64_t now_ns;
+	unsigned int misecs, count, rate;
+	struct strbuf buf = STRBUF_INIT;
 
 	if (!progress)
 		return;
 	tp = progress->throughput;
 
-	gettimeofday(&tv, NULL);
+	now_ns = getnanotime();
 
 	if (!tp) {
 		progress->throughput = tp = calloc(1, sizeof(*tp));
 		if (tp) {
 			tp->prev_total = tp->curr_total = total;
-			tp->prev_tv = tv;
+			tp->prev_ns = now_ns;
 		}
 		return;
 	}
 	tp->curr_total = total;
 
+	/* only update throughput every 0.5 s */
+	if (now_ns - tp->prev_ns <= 500000000)
+		return;
+
 	/*
-	 * We have x = bytes and y = microsecs.  We want z = KiB/s:
+	 * We have x = bytes and y = nanosecs.  We want z = KiB/s:
 	 *
-	 *	z = (x / 1024) / (y / 1000000)
-	 *	z = x / y * 1000000 / 1024
-	 *	z = x / (y * 1024 / 1000000)
+	 *	z = (x / 1024) / (y / 1000000000)
+	 *	z = x / y * 1000000000 / 1024
+	 *	z = x / (y * 1024 / 1000000000)
 	 *	z = x / y'
 	 *
 	 * To simplify things we'll keep track of misecs, or 1024th of a sec
 	 * obtained with:
 	 *
-	 *	y' = y * 1024 / 1000000
-	 *	y' = y / (1000000 / 1024)
-	 *	y' = y / 977
+	 *	y' = y * 1024 / 1000000000
+	 *	y' = y * (2^10 / 2^42) * (2^42 / 1000000000)
+	 *	y' = y / 2^32 * 4398
+	 *	y' = (y * 4398) >> 32
 	 */
-	misecs = (tv.tv_sec - tp->prev_tv.tv_sec) * 1024;
-	misecs += (int)(tv.tv_usec - tp->prev_tv.tv_usec) / 977;
+	misecs = ((now_ns - tp->prev_ns) * 4398) >> 32;
 
-	if (misecs > 512) {
-		struct strbuf buf = STRBUF_INIT;
-		unsigned int count, rate;
+	count = total - tp->prev_total;
+	tp->prev_total = total;
+	tp->prev_ns = now_ns;
+	tp->avg_bytes += count;
+	tp->avg_misecs += misecs;
+	rate = tp->avg_bytes / tp->avg_misecs;
+	tp->avg_bytes -= tp->last_bytes[tp->idx];
+	tp->avg_misecs -= tp->last_misecs[tp->idx];
+	tp->last_bytes[tp->idx] = count;
+	tp->last_misecs[tp->idx] = misecs;
+	tp->idx = (tp->idx + 1) % TP_IDX_MAX;
 
-		count = total - tp->prev_total;
-		tp->prev_total = total;
-		tp->prev_tv = tv;
-		tp->avg_bytes += count;
-		tp->avg_misecs += misecs;
-		rate = tp->avg_bytes / tp->avg_misecs;
-		tp->avg_bytes -= tp->last_bytes[tp->idx];
-		tp->avg_misecs -= tp->last_misecs[tp->idx];
-		tp->last_bytes[tp->idx] = count;
-		tp->last_misecs[tp->idx] = misecs;
-		tp->idx = (tp->idx + 1) % TP_IDX_MAX;
-
-		throughput_string(&buf, total, rate);
-		strncpy(tp->display, buf.buf, sizeof(tp->display));
-		strbuf_release(&buf);
-		if (progress->last_value != -1 && progress_update)
-			display(progress, progress->last_value, NULL);
-	}
+	throughput_string(&buf, total, rate);
+	strncpy(tp->display, buf.buf, sizeof(tp->display));
+	strbuf_release(&buf);
+	if (progress->last_value != -1 && progress_update)
+		display(progress, progress->last_value, NULL);
 }
 
 int display_progress(struct progress *progress, unsigned n)
-- 
2.0.0.406.ge74f8ff

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