[PATCH] net/core/net-procfs: use seq_put_decimal_ull_width() for decimal values in /proc/net/dev

[David Wang <00107082@163.com>]

seq_printf() is costy, when reading /proc/net/dev, profiling indicates
about 13% samples of seq_printf():
	dev_seq_show(98.350% 428046/435229)
	    dev_seq_printf_stats(99.777% 427092/428046)
		dev_get_stats(86.121% 367814/427092)
		    rtl8169_get_stats64(98.519% 362365/367814)
		    dev_fetch_sw_netstats(0.554% 2038/367814)
		    loopback_get_stats64(0.250% 919/367814)
		    dev_get_tstats64(0.077% 284/367814)
		    netdev_stats_to_stats64(0.051% 189/367814)
		    _find_next_bit(0.029% 106/367814)
		seq_printf(13.719% 58594/427092)
And on a system with one wireless interface, timing for 1 million rounds of
stress reading /proc/net/dev:
	real	0m51.828s
	user	0m0.225s
	sys	0m51.671s
On average, reading /proc/net/dev takes ~0.051ms

With this patch, extra costs parsing format string by seq_printf() can be
optimized out, and the timing for 1 million rounds of read is:
	real	0m49.127s
	user	0m0.295s
	sys	0m48.552s
On average, ~0.048ms reading /proc/net/dev, a ~6% improvement.

Even though dev_get_stats() takes up the majority of the reading process,
the improvement is still significant;
And the improvement may vary with the physical interface on the system.

Signed-off-by: David Wang <00107082@163.com>
---
 net/core/net-procfs.c | 37 ++++++++++++++++++++-----------------
 1 file changed, 20 insertions(+), 17 deletions(-)

diff --git a/net/core/net-procfs.c b/net/core/net-procfs.c
index fa6d3969734a..a0d6c5b32b58 100644
--- a/net/core/net-procfs.c
+++ b/net/core/net-procfs.c
@@ -46,23 +46,26 @@ static void dev_seq_printf_stats(struct seq_file *seq, struct net_device *dev)
 	struct rtnl_link_stats64 temp;
 	const struct rtnl_link_stats64 *stats = dev_get_stats(dev, &temp);
 
-	seq_printf(seq, "%6s: %7llu %7llu %4llu %4llu %4llu %5llu %10llu %9llu "
-		   "%8llu %7llu %4llu %4llu %4llu %5llu %7llu %10llu\n",
-		   dev->name, stats->rx_bytes, stats->rx_packets,
-		   stats->rx_errors,
-		   stats->rx_dropped + stats->rx_missed_errors,
-		   stats->rx_fifo_errors,
-		   stats->rx_length_errors + stats->rx_over_errors +
-		    stats->rx_crc_errors + stats->rx_frame_errors,
-		   stats->rx_compressed, stats->multicast,
-		   stats->tx_bytes, stats->tx_packets,
-		   stats->tx_errors, stats->tx_dropped,
-		   stats->tx_fifo_errors, stats->collisions,
-		   stats->tx_carrier_errors +
-		    stats->tx_aborted_errors +
-		    stats->tx_window_errors +
-		    stats->tx_heartbeat_errors,
-		   stats->tx_compressed);
+	seq_printf(seq, "%6s:", dev->name);
+	seq_put_decimal_ull_width(seq, " ", stats->rx_bytes, 7);
+	seq_put_decimal_ull_width(seq, " ", stats->rx_packets, 7);
+	seq_put_decimal_ull_width(seq, " ", stats->rx_errors, 4);
+	seq_put_decimal_ull_width(seq, " ", stats->rx_dropped + stats->rx_missed_errors, 4);
+	seq_put_decimal_ull_width(seq, " ", stats->rx_fifo_errors, 4);
+	seq_put_decimal_ull_width(seq, " ", stats->rx_length_errors + stats->rx_over_errors +
+				  stats->rx_crc_errors + stats->rx_frame_errors, 5);
+	seq_put_decimal_ull_width(seq, " ", stats->rx_compressed, 10);
+	seq_put_decimal_ull_width(seq, " ", stats->multicast, 9);
+	seq_put_decimal_ull_width(seq, " ", stats->tx_bytes, 8);
+	seq_put_decimal_ull_width(seq, " ", stats->tx_packets, 7);
+	seq_put_decimal_ull_width(seq, " ", stats->tx_errors, 4);
+	seq_put_decimal_ull_width(seq, " ", stats->tx_dropped, 4);
+	seq_put_decimal_ull_width(seq, " ", stats->tx_fifo_errors, 4);
+	seq_put_decimal_ull_width(seq, " ", stats->collisions, 5);
+	seq_put_decimal_ull_width(seq, " ", stats->tx_carrier_errors + stats->tx_aborted_errors +
+				  stats->tx_window_errors + stats->tx_heartbeat_errors, 7);
+	seq_put_decimal_ull_width(seq, " ", stats->tx_compressed, 10);
+	seq_putc(seq, '\n');
 }
 
 /*
-- 
2.39.2