On 9/6/17, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > On Tue, 5 Sep 2017 22:05:00 +0300 Alexey Dobriyan <adobriyan@xxxxxxxxx> > wrote: > >> Implement system call for bulk retrieveing of pids in binary form. >> >> Using /proc is slower than necessary: 3 syscalls + another 3 for each >> thread + >> converting with atoi(). >> >> /proc may be not mounted especially in containers. Natural extension of >> hidepid=2 efforts is to not mount /proc at all. >> >> It could be used by programs like ps, top or CRIU. Speed increase will >> become more drastic once combined with bulk retrieval of process >> statistics. > > The patches are performance optimizations, but their changelogs contain > no performance measurements! > > Demonstration of some compelling real-world performance benefits would > help things along a lot. I forgot the sheet with numbers at work. :^) They're very embarrassing for /proc. pidmap: N=1<<16 times ~130 processes (~250 task_structs) on a regular desktop system opendir + readdir + closedir /proc + the same for every /proc/$PID/task (roughly what htop(1) does) vs pidmap /proc 16.80+-0.73% pidmap 0.06+-0.31% fdmap: N=1<<22 times 4 opened descriptors (0, 1, 2, 3) opendir+readdir+closedir /proc/self/fd (lsof(1)) vs fdmap /proc 8.31+-0.37% fdmap 0.32+-0.72% Currently performance improvements may not be huge or even visible. That's because programs like ps/top/lsof _have_ to use /proc to retrieve other information. If combined with bulk taskstats-ish retrieval interfaces they should run around /proc.
#include <sys/types.h> #include <stdio.h> #include <dirent.h> #include <stdlib.h> #include <unistd.h> void f(void) { DIR *d; struct dirent *de; d = opendir("/proc/"); while ((de = readdir(d))) { if ('1' <= de->d_name[0] && de->d_name[0] <= '9') { int pid = atoi(de->d_name); char buf[32]; DIR *dt; struct dirent *dte; snprintf(buf, sizeof(buf), "/proc/%d/task", pid); dt = opendir(buf); readdir(dt); readdir(dt); while ((dte = readdir(dt))) { int tid = atoi(dte->d_name); asm volatile ("" :: "g" (&tid) : "memory"); } closedir(dt); } } closedir(d); } static inline long sys_pidmap(int *pid, unsigned int n, int start) { register long r10 asm ("r10") = 0; long rv; asm volatile ( "syscall" : "=a" (rv) : "0" (333), "D" (pid), "S" (n), "d" (start), "r" (r10) : "rcx", "r11", "cc", "memory" ); return rv; } void g(void) { int pid[1024]; sys_pidmap(pid, sizeof(pid)/sizeof(pid[0]), 0); } int main(void) { unsigned int i; // for (i = 0; i < (1<<16); i++) // f(); for (i = 0; i < (1<<16); i++) g(); return 0; }
#include <sys/types.h> #include <dirent.h> #include <stdlib.h> #include <unistd.h> void f(void) { DIR *d; struct dirent *de; d = opendir("/proc/self/fd"); while ((de = readdir(d))) { int fd = atoi(de->d_name); asm volatile ("" :: "g" (&fd) : "memory"); } closedir(d); } static inline long sys_fdmap(int pid, int *fd, unsigned int n, int start) { register long r10 asm ("r10") = start; register long r8 asm ("r8") = 0; long rv; asm volatile ( "syscall" : "=a" (rv) : "0" (334), "D" (pid), "S" (fd), "d" (n), "r" (r10), "r" (r8) : "rcx", "r11", "cc", "memory" ); return rv; } void g(void) { int fd[1024]; sys_fdmap(0, fd, sizeof(fd)/sizeof(fd[0]), 0); } int main(void) { unsigned int i; // for (i = 0; i < (1<<22); i++) // f(); dup(0); for (i = 0; i < (1<<22); i++) g(); return 0; }