forked from luck/tmp_suning_uos_patched
68ba0326b4
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>
|
||
|---|---|---|
| .. | ||
| kasan | ||
| backing-dev.c | ||
| balloon_compaction.c | ||
| bootmem.c | ||
| cleancache.c | ||
| cma_debug.c | ||
| cma.c | ||
| cma.h | ||
| compaction.c | ||
| debug_page_ref.c | ||
| debug.c | ||
| dmapool.c | ||
| early_ioremap.c | ||
| fadvise.c | ||
| failslab.c | ||
| filemap.c | ||
| frame_vector.c | ||
| frontswap.c | ||
| gup.c | ||
| highmem.c | ||
| huge_memory.c | ||
| hugetlb_cgroup.c | ||
| hugetlb.c | ||
| hwpoison-inject.c | ||
| init-mm.c | ||
| internal.h | ||
| interval_tree.c | ||
| Kconfig | ||
| Kconfig.debug | ||
| khugepaged.c | ||
| kmemcheck.c | ||
| kmemleak-test.c | ||
| kmemleak.c | ||
| ksm.c | ||
| list_lru.c | ||
| maccess.c | ||
| madvise.c | ||
| Makefile | ||
| memblock.c | ||
| memcontrol.c | ||
| memory_hotplug.c | ||
| memory-failure.c | ||
| memory.c | ||
| mempolicy.c | ||
| mempool.c | ||
| memtest.c | ||
| migrate.c | ||
| mincore.c | ||
| mlock.c | ||
| mm_init.c | ||
| mmap.c | ||
| mmu_context.c | ||
| mmu_notifier.c | ||
| mmzone.c | ||
| mprotect.c | ||
| mremap.c | ||
| msync.c | ||
| nobootmem.c | ||
| nommu.c | ||
| oom_kill.c | ||
| page_alloc.c | ||
| page_counter.c | ||
| page_ext.c | ||
| page_idle.c | ||
| page_io.c | ||
| page_isolation.c | ||
| page_owner.c | ||
| page_poison.c | ||
| page-writeback.c | ||
| pagewalk.c | ||
| percpu-km.c | ||
| percpu-vm.c | ||
| percpu.c | ||
| pgtable-generic.c | ||
| process_vm_access.c | ||
| quicklist.c | ||
| readahead.c | ||
| rmap.c | ||
| shmem.c | ||
| slab_common.c | ||
| slab.c | ||
| slab.h | ||
| slob.c | ||
| slub.c | ||
| sparse-vmemmap.c | ||
| sparse.c | ||
| swap_cgroup.c | ||
| swap_state.c | ||
| swap.c | ||
| swapfile.c | ||
| truncate.c | ||
| usercopy.c | ||
| userfaultfd.c | ||
| util.c | ||
| vmacache.c | ||
| vmalloc.c | ||
| vmpressure.c | ||
| vmscan.c | ||
| vmstat.c | ||
| workingset.c | ||
| z3fold.c | ||
| zbud.c | ||
| zpool.c | ||
| zsmalloc.c | ||
| zswap.c | ||