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Message-Id: <20241108054500.4251-1-00107082@163.com>
Date: Fri, 8 Nov 2024 13:45:00 +0800
From: David Wang <00107082@....com>
To: axboe@...nel.dk
Cc: linux-block@...r.kernel.org,
linux-kernel@...r.kernel.org,
David Wang <00107082@....com>
Subject: [PATCH] block:genhd:/proc/diskstats: use seq_put_decimal_ull for decimal values
seq_printf is costy, 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: David Wang <00107082@....com>
---
block/genhd.c | 63 ++++++++++++++++++++++++---------------------------
1 file changed, 29 insertions(+), 34 deletions(-)
diff --git a/block/genhd.c b/block/genhd.c
index 1c05dd4c6980..72f481a82fa4 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -1264,40 +1264,35 @@ 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] +
- 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)
- );
+ 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));
+ 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();
--
2.39.2
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