payload: {"push_id":4228624867,"size":1,"distinct_size":1,"ref":"refs/heads/lineage-17.0","head":"0409588ed587bd497aa01249d8902ad469a7bd48","before":"3815afa71a463e3617d72acb12e0f2c92fbac11b","commits":[{"sha":"0409588ed587bd497aa01249d8902ad469a7bd48","author":{"name":"Francisco Franco","email":"42480b5f4d505650064e5081b85d867a03559887@gmail.com"},"message":"proc: much faster /proc/vmstat\n\nEvery current KDE system has process named ksysguardd polling files\nbelow once in several seconds:\n\n\t$ strace -e trace=open -p $(pidof ksysguardd)\n\tProcess 1812 attached\n\topen(\"/etc/mtab\", O_RDONLY|O_CLOEXEC)   = 8\n\topen(\"/etc/mtab\", O_RDONLY|O_CLOEXEC)   = 8\n\topen(\"/proc/net/dev\", O_RDONLY)         = 8\n\topen(\"/proc/net/wireless\", O_RDONLY)    = -1 ENOENT (No such file or directory)\n\topen(\"/proc/stat\", O_RDONLY)            = 8\n\topen(\"/proc/vmstat\", O_RDONLY)          = 8\n\nHell knows what it is doing but speed up reading /proc/vmstat by 33%!\n\nBenchmark is open+read+close 1.000.000 times.\n\n\t\t\tBEFORE\n$ perf stat -r 10 taskset -c 3 ./proc-vmstat\n\n Performance counter stats for 'taskset -c 3 ./proc-vmstat' (10 runs):\n\n      13146.768464      task-clock (msec)         #    0.960 CPUs utilized            ( +-  0.60% )\n                15      context-switches          #    0.001 K/sec                    ( +-  1.41% )\n                 1      cpu-migrations            #    0.000 K/sec                    ( +- 11.11% )\n               104      page-faults               #    0.008 K/sec                    ( +-  0.57% )\n    45,489,799,349      cycles                    #    3.460 GHz                      ( +-  0.03% )\n     9,970,175,743      stalled-cycles-frontend   #   21.92% frontend cycles idle     ( +-  0.10% )\n     2,800,298,015      stalled-cycles-backend    #   6.16% backend cycles idle       ( +-  0.32% )\n    79,241,190,850      instructions              #    1.74  insn per cycle\n                                                  #    0.13  stalled cycles per insn  ( +-  0.00% )\n    17,616,096,146      branches                  # 1339.956 M/sec                    ( +-  0.00% )\n       176,106,232      branch-misses             #    1.00% of all branches          ( +-  0.18% )\n\n      13.691078109 seconds time elapsed                                          ( +-  0.03% )\n      ^^^^^^^^^^^^\n\n\t\t\tAFTER\n$ perf stat -r 10 taskset -c 3 ./proc-vmstat\n\n Performance counter stats for 'taskset -c 3 ./proc-vmstat' (10 runs):\n\n       8688.353749      task-clock (msec)         #    0.950 CPUs utilized            ( +-  1.25% )\n                10      context-switches          #    0.001 K/sec                    ( +-  2.13% )\n                 1      cpu-migrations            #    0.000 K/sec\n               104      page-faults               #    0.012 K/sec                    ( +-  0.56% )\n    30,384,010,730      cycles                    #    3.497 GHz                      ( +-  0.07% )\n    12,296,259,407      stalled-cycles-frontend   #   40.47% frontend cycles idle     ( +-  0.13% )\n     3,370,668,651      stalled-cycles-backend    #  11.09% backend cycles idle       ( +-  0.69% )\n    28,969,052,879      instructions              #    0.95  insn per cycle\n                                                  #    0.42  stalled cycles per insn  ( +-  0.01% )\n     6,308,245,891      branches                  #  726.058 M/sec                    ( +-  0.00% )\n       214,685,502      branch-misses             #    3.40% of all branches          ( +-  0.26% )\n\n       9.146081052 seconds time elapsed                                          ( +-  0.07% )\n       ^^^^^^^^^^^\n\nvsnprintf() is slow because:\n\n1. format_decode() is busy looking for format specifier: 2 branches\n   per character (not in this case, but in others)\n\n2. approximately million branches while parsing format mini language\n   and everywhere\n\n3.  just look at what string() does /proc/vmstat is good case because\n   most of its content are strings\n\nLink: http://lkml.kernel.org/r/20160806125455.GA1187@p183.telecom.by\nSigned-off-by: Alexey Dobriyan <adobriyan@gmail.com>\nCc: Joe Perches <joe@perches.com>\nCc: Andi Kleen <andi@firstfloor.org>\nCc: Al Viro <viro@zeniv.linux.org.uk>\nSigned-off-by: Andrew Morton <akpm@linux-foundation.org>\nSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>\nSigned-off-by: Francisco Franco <franciscofranco.1990@gmail.com>\nSigned-off-by: 1bdellatiF <ptaoubi@gmail.com>","distinct":true,"url":"https://api.github.com/repos/1bdellatiF/android_kernel_samsung_msm8974/commits/0409588ed587bd497aa01249d8902ad469a7bd48"}]}
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