Commit bda9c7d9 authored by David Wang's avatar David Wang Committed by Jens Axboe
Browse files

block/genhd: use seq_put_decimal_ull for diskstats decimal values 



seq_printf is costly. For each block device, 19 decimal values are
yielded in /proc/diskstats via seq_printf. On a system with 16 logical
block devices, profiling for open/read/close sequences shows seq_printf
took ~75% samples of diskstats_show:

	diskstats_show(92.626% 2269372/2450040)
	    seq_printf(76.026% 1725313/2269372)
		vsnprintf(99.163% 1710866/1725313)
		    format_decode(26.597% 455040/1710866)
		    number(19.554% 334542/1710866)
		    memcpy_orig(4.183% 71570/1710866)
			...
		srso_return_thunk(0.009% 148/1725313)
	    part_stat_read_all(8.030% 182236/2269372)

One million rounds of open/read/close /proc/diskstats takes:

	real	0m37.687s
	user	0m0.264s
	sys	0m32.911s
On average, each sequence tooks ~0.032ms

With this patch, most decimal values are yield via seq_put_decimal_ull,
performance is significantly improved:

	real	0m20.792s
	user	0m0.316s
	sys	0m20.463s
On average, each sequence tooks ~0.020ms, a ~37.5% improvement.

Signed-off-by: default avatarDavid Wang <00107082@163.com>
Link: https://lore.kernel.org/r/20241108054500.4251-1-00107082@163.com


Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 00e8d290

block/genhd.c

+29 −34
Original line number Diff line number Diff line
@@ -1291,40 +1291,35 @@ static int diskstats_show(struct seq_file *seqf, void *v) 
			part_stat_unlock();

		}

		part_stat_read_all(hd, &stat);

		seq_printf(seqf, "%4d %7d %pg "

			   "%lu %lu %lu %u "

			   "%lu %lu %lu %u "

			   "%u %u %u "

			   "%lu %lu %lu %u "

			   "%lu %u"

			   "\n",

			   MAJOR(hd->bd_dev), MINOR(hd->bd_dev), hd,

			   stat.ios[STAT_READ],

			   stat.merges[STAT_READ],

			   stat.sectors[STAT_READ],

			   (unsigned int)div_u64(stat.nsecs[STAT_READ],

							NSEC_PER_MSEC),

			   stat.ios[STAT_WRITE],

			   stat.merges[STAT_WRITE],

			   stat.sectors[STAT_WRITE],

			   (unsigned int)div_u64(stat.nsecs[STAT_WRITE],

							NSEC_PER_MSEC),

			   inflight,

			   jiffies_to_msecs(stat.io_ticks),

			   (unsigned int)div_u64(stat.nsecs[STAT_READ] +

		seq_put_decimal_ull_width(seqf, "",  MAJOR(hd->bd_dev), 4);

		seq_put_decimal_ull_width(seqf, " ", MINOR(hd->bd_dev), 7);

		seq_printf(seqf, " %pg", hd);

		seq_put_decimal_ull(seqf, " ", stat.ios[STAT_READ]);

		seq_put_decimal_ull(seqf, " ", stat.merges[STAT_READ]);

		seq_put_decimal_ull(seqf, " ", stat.sectors[STAT_READ]);

		seq_put_decimal_ull(seqf, " ", (unsigned int)div_u64(stat.nsecs[STAT_READ],

								     NSEC_PER_MSEC));

		seq_put_decimal_ull(seqf, " ", stat.ios[STAT_WRITE]);

		seq_put_decimal_ull(seqf, " ", stat.merges[STAT_WRITE]);

		seq_put_decimal_ull(seqf, " ", stat.sectors[STAT_WRITE]);

		seq_put_decimal_ull(seqf, " ", (unsigned int)div_u64(stat.nsecs[STAT_WRITE],

								     NSEC_PER_MSEC));

		seq_put_decimal_ull(seqf, " ", inflight);

		seq_put_decimal_ull(seqf, " ", jiffies_to_msecs(stat.io_ticks));

		seq_put_decimal_ull(seqf, " ", (unsigned int)div_u64(stat.nsecs[STAT_READ] +

								     stat.nsecs[STAT_WRITE] +

								     stat.nsecs[STAT_DISCARD] +

								     stat.nsecs[STAT_FLUSH],

							NSEC_PER_MSEC),

			   stat.ios[STAT_DISCARD],

			   stat.merges[STAT_DISCARD],

			   stat.sectors[STAT_DISCARD],

			   (unsigned int)div_u64(stat.nsecs[STAT_DISCARD],

						 NSEC_PER_MSEC),

			   stat.ios[STAT_FLUSH],

			   (unsigned int)div_u64(stat.nsecs[STAT_FLUSH],

						 NSEC_PER_MSEC)

			);

								     NSEC_PER_MSEC));

		seq_put_decimal_ull(seqf, " ", stat.ios[STAT_DISCARD]);

		seq_put_decimal_ull(seqf, " ", stat.merges[STAT_DISCARD]);

		seq_put_decimal_ull(seqf, " ", stat.sectors[STAT_DISCARD]);

		seq_put_decimal_ull(seqf, " ", (unsigned int)div_u64(stat.nsecs[STAT_DISCARD],

								     NSEC_PER_MSEC));

		seq_put_decimal_ull(seqf, " ", stat.ios[STAT_FLUSH]);

		seq_put_decimal_ull(seqf, " ", (unsigned int)div_u64(stat.nsecs[STAT_FLUSH],

								     NSEC_PER_MSEC));

		seq_putc(seqf, '\n');

	}

	rcu_read_unlock();