This is a note to let you know that I've just added the patch titled

proc: much faster /proc/vmstat

to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: proc-much-faster-proc-vmstat.patch and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From 68ba0326b4e14988f9e0c24a6e12a85cf2acd1ca Mon Sep 17 00:00:00 2001

From: Alexey Dobriyan adobriyan@gmail.com Date: Fri, 7 Oct 2016 17:02:14 -0700 Subject: proc: much faster /proc/vmstat

From: Alexey Dobriyan adobriyan@gmail.com

commit 68ba0326b4e14988f9e0c24a6e12a85cf2acd1ca upstream.

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: Mel Gorman mgorman@suse.de Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

--- mm/vmstat.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/mm/vmstat.c +++ b/mm/vmstat.c @@ -1351,7 +1351,9 @@ static int vmstat_show(struct seq_file * 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; }

Patches currently in stable-queue which might be from adobriyan@gmail.com are

queue-4.4/proc-much-faster-proc-vmstat.patch