hostside/rtprio.c

   1 /*
   2  * realtime
   3  * realtime priority
   4  */
   5
   6 #include "realtime.h"
   7
   8 #include <sys/resource.h>
   9 #include <signal.h>
  10 #include <time.h>
  11
  12 #include <sched.h>
  13
  14 /*---------- !ALL(MEM): prevent us eating all RAM ----------*/
  15
  16 static void rtf_limit_MEM(void) {
  17   int r;
  18   struct rlimit64 rl;
  19   r= getrlimit64(RLIMIT_MEMLOCK,&rl);  if (r) diee("getrlimit RLIMIT_MEMLOCK");
  20   rl.rlim_cur= 4*1024*1024;
  21   r= setrlimit64(RLIMIT_MEMLOCK,&rl);  if (r) diee("setrlimit RLIMIT_MEMLOCK");
  22 }
  23
  24 /*---------- MEM: lock us into memory ----------*/
  25
  26 static void rtf_acquire_MEM(void) {
  27   int r;
  28   r= mlockall(MCL_CURRENT|MCL_FUTURE);  if (r) diee("mlockall");
  29 }
  30
  31 /*---------- !ALL(CPU): use SIGXCPU to detect us spinning ----------*/
  32
  33 #define MAX_CPU_CREDIT 5 /* max burst of 5 seconds */
  34 #define MAX_CPU_NTH 2 /* allow up to 50% usage, sustained */
  35
  36 static time_t now, last;
  37 static struct rlimit rlcpu;
  38 static struct sigaction sa_xcpu;
  39
  40 static void write_stderr(const char *m, int l) { write(2,m,l); }
  41
  42 static void cpulim_bomb(const char *what) __attribute__((noreturn));
  43 static void cpulim_bomb(const char *what) {
  44   static const char m[]= "realtime: cpu limitation failure: ";
  45   int e;
  46   const char *s;
  47
  48   e= errno;
  49   write_stderr(m,sizeof(m)-1);
  50   write_stderr(what,strlen(what));
  51   write_stderr(": ",2);
  52
  53   s= strerror(e);
  54   write_stderr(s,strlen(s));
  55   write_stderr("\n",1);
  56   exit(-127);
  57 }
  58
  59 static const char *cpulim_gnow(void) { /* returns what failed */
  60   if (time(&now) == (time_t)-1) return "time(2)";
  61   return 0;
  62 }
  63
  64 static const char *cpulim_makepending(void) { /* returns what failed */
  65   int r;
  66   last= now;
  67   r= sigaction(SIGXCPU, &sa_xcpu, 0);  if (r) return "sigaction SIGXCPU";
  68   r= setrlimit(RLIMIT_CPU, &rlcpu);    if (r) return "setrlimit RLIMIT_CPU";
  69   return 0;
  70 }
  71
  72 static void cpulim_exceeded(void) {
  73   static const char m[]= "realtime: cpu limit exceeded\n";
  74   write_stderr(m,sizeof(m)-1);
  75   raise(SIGXCPU);
  76   abort();
  77 }
  78
  79 static void xcpuhandler(int ignored) {
  80   int credit;
  81   const char *whatfailed;
  82
  83   whatfailed= cpulim_gnow();
  84   if (whatfailed) goto fail;
  85
  86   credit= (now - last)/MAX_CPU_NTH;
  87   if (credit <= 0) cpulim_exceeded();
  88   if (credit > MAX_CPU_CREDIT) credit= MAX_CPU_CREDIT;
  89   rlcpu.rlim_cur += credit;
  90
  91   whatfailed= cpulim_makepending();
  92   if (whatfailed) goto fail;
  93   return;
  94
  95 fail:
  96   cpulim_bomb(whatfailed);
  97 }
  98
  99 static void rtf_limit_CPU(void) {
 100   int r;
 101   const char *whatfailed;
 102
 103   memset(&sa_xcpu,0,sizeof(sa_xcpu));
 104   sa_xcpu.sa_handler= xcpuhandler;
 105   sigemptyset(&sa_xcpu.sa_mask);
 106   sa_xcpu.sa_flags= SA_RESETHAND | SA_RESTART | SA_NODEFER;
 107
 108   r= getrlimit(RLIMIT_CPU, &rlcpu);
 109   if (r) { whatfailed= "getrlimit RLIMIT_CPU"; goto fail; }
 110
 111   whatfailed= cpulim_gnow();
 112   if (whatfailed) goto fail;
 113
 114   rlcpu.rlim_cur= MAX_CPU_CREDIT;
 115
 116   whatfailed= cpulim_makepending();
 117   if (whatfailed) goto fail;
 118   return;
 119
 120 fail:
 121   diee("prepare cpu limiter: %s",whatfailed);
 122 }
 123
 124 /*---------- CPU: set hard scheduling priority ----------*/
 125
 126 static void rtf_acquire_CPU(void) {
 127   pid_t child;
 128
 129   child= fork();
 130   if (child<0) diee("fork for auth-sched-setscheduler");
 131
 132   if (!child) {
 133     execlp("auth-sched-setscheduler",
 134            "auth-sched-setscheduler","fifo","10",(char*)0);
 135     diee("exec auth-sched-setscheduler");
 136   }
 137   mwaitpid(child, "auth-sched-setscheduler");
 138 }
 139
 140 /*---------- core ----------*/
 141
 142 unsigned rtfeats_use= RTFEAT_DEFAULTS;
 143
 144 void realtime_priority(void) {
 145 #define RESOURCE(NAME)                                          \
 146   if (rtfeats_use & RTFEAT_##NAME) {                            \
 147     if (!(rtfeats_use & RTFEAT_ALL(NAME))) rtf_limit_##NAME();  \
 148     rtf_acquire_##NAME();                                       \
 149   }
 150   RESOURCE(MEM);
 151   RESOURCE(CPU);
 152 }