From: Alexey Dobriyan adobriyan@gmail.com
This patch has been added to the 4.1 stable tree. If you have any objections, please let us know.
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[ Upstream commit 68ba0326b4e14988f9e0c24a6e12a85cf2acd1ca ]
Every current KDE system has process named ksysguardd polling files below once in several seconds:
$ strace -e trace=open -p $(pidof ksysguardd) Process 1812 attached open("/etc/mtab", O_RDONLY|O_CLOEXEC) = 8 open("/etc/mtab", O_RDONLY|O_CLOEXEC) = 8 open("/proc/net/dev", O_RDONLY) = 8 open("/proc/net/wireless", O_RDONLY) = -1 ENOENT (No such file or directory) open("/proc/stat", O_RDONLY) = 8 open("/proc/vmstat", O_RDONLY) = 8
Hell knows what it is doing but speed up reading /proc/vmstat by 33%!
Benchmark is open+read+close 1.000.000 times.
BEFORE $ perf stat -r 10 taskset -c 3 ./proc-vmstat
Performance counter stats for 'taskset -c 3 ./proc-vmstat' (10 runs):
13146.768464 task-clock (msec) # 0.960 CPUs utilized ( +- 0.60% ) 15 context-switches # 0.001 K/sec ( +- 1.41% ) 1 cpu-migrations # 0.000 K/sec ( +- 11.11% ) 104 page-faults # 0.008 K/sec ( +- 0.57% ) 45,489,799,349 cycles # 3.460 GHz ( +- 0.03% ) 9,970,175,743 stalled-cycles-frontend # 21.92% frontend cycles idle ( +- 0.10% ) 2,800,298,015 stalled-cycles-backend # 6.16% backend cycles idle ( +- 0.32% ) 79,241,190,850 instructions # 1.74 insn per cycle # 0.13 stalled cycles per insn ( +- 0.00% ) 17,616,096,146 branches # 1339.956 M/sec ( +- 0.00% ) 176,106,232 branch-misses # 1.00% of all branches ( +- 0.18% )
13.691078109 seconds time elapsed ( +- 0.03% ) ^^^^^^^^^^^^
AFTER $ perf stat -r 10 taskset -c 3 ./proc-vmstat
Performance counter stats for 'taskset -c 3 ./proc-vmstat' (10 runs):
8688.353749 task-clock (msec) # 0.950 CPUs utilized ( +- 1.25% ) 10 context-switches # 0.001 K/sec ( +- 2.13% ) 1 cpu-migrations # 0.000 K/sec 104 page-faults # 0.012 K/sec ( +- 0.56% ) 30,384,010,730 cycles # 3.497 GHz ( +- 0.07% ) 12,296,259,407 stalled-cycles-frontend # 40.47% frontend cycles idle ( +- 0.13% ) 3,370,668,651 stalled-cycles-backend # 11.09% backend cycles idle ( +- 0.69% ) 28,969,052,879 instructions # 0.95 insn per cycle # 0.42 stalled cycles per insn ( +- 0.01% ) 6,308,245,891 branches # 726.058 M/sec ( +- 0.00% ) 214,685,502 branch-misses # 3.40% of all branches ( +- 0.26% )
9.146081052 seconds time elapsed ( +- 0.07% ) ^^^^^^^^^^^
vsnprintf() is slow because:
1. format_decode() is busy looking for format specifier: 2 branches per character (not in this case, but in others)
2. approximately million branches while parsing format mini language and everywhere
3. just look at what string() does /proc/vmstat is good case because most of its content are strings
Link: http://lkml.kernel.org/r/20160806125455.GA1187@p183.telecom.by Signed-off-by: Alexey Dobriyan adobriyan@gmail.com Cc: Joe Perches joe@perches.com Cc: Andi Kleen andi@firstfloor.org Cc: Al Viro viro@zeniv.linux.org.uk Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Sasha Levin alexander.levin@microsoft.com --- mm/vmstat.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/mm/vmstat.c b/mm/vmstat.c index 4f5cd974e11a..9b525cd66ca6 100644 --- a/mm/vmstat.c +++ b/mm/vmstat.c @@ -1326,7 +1326,9 @@ static int vmstat_show(struct seq_file *m, void *arg) unsigned long *l = arg; unsigned long off = l - (unsigned long *)m->private;
- seq_printf(m, "%s %lu\n", vmstat_text[off], *l); + seq_puts(m, vmstat_text[off]); + seq_put_decimal_ull(m, ' ', *l); + seq_putc(m, '\n'); return 0; }