From: Leo Alterman Date: Tue, 7 Aug 2012 23:36:27 +0000 (-0700) Subject: timeval: On Linux x86-64 systems refresh time whenever it is requested. X-Git-Url: https://pintos-os.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=49635519bae2c14e44744825c907ccee9216bf90;p=openvswitch timeval: On Linux x86-64 systems refresh time whenever it is requested. 64-bit Linux appears to avoid syscalls for clock_gettime(), so we can get higher resolution timing and avoid having a timer firing off SIGALRM without introducing extra overhead. Signed-off-by: Leo Alterman --- diff --git a/lib/timeval.c b/lib/timeval.c index d29b6618..3d339e4e 100644 --- a/lib/timeval.c +++ b/lib/timeval.c @@ -40,7 +40,7 @@ VLOG_DEFINE_THIS_MODULE(timeval); * to CLOCK_REALTIME. */ static clockid_t monotonic_clock; -/* Has a timer tick occurred? +/* Has a timer tick occurred? Only relevant if CACHE_TIME is 1. * * We initialize these to true to force time_init() to get called on the first * call to time_msec() or another function that queries the current time. */ @@ -94,8 +94,11 @@ time_init(void) VLOG_DBG("monotonic timer not available"); } - set_up_signal(SA_RESTART); - set_up_timer(); + if (CACHE_TIME) { + set_up_signal(SA_RESTART); + set_up_timer(); + } + boot_time = time_msec(); } @@ -168,7 +171,16 @@ void time_postfork(void) { time_init(); - set_up_timer(); + + if (CACHE_TIME) { + set_up_timer(); + } else { + /* If we are not caching kernel time, the only reason the timer should + * exist is if time_alarm() was called and deadline is set */ + if (deadline != TIME_MIN) { + set_up_timer(); + } + } } static void @@ -199,7 +211,9 @@ refresh_monotonic(void) /* Forces a refresh of the current time from the kernel. It is not usually * necessary to call this function, since the time will be refreshed - * automatically at least every TIME_UPDATE_INTERVAL milliseconds. */ + * automatically at least every TIME_UPDATE_INTERVAL milliseconds. If + * CACHE_TIME is 0, we will always refresh the current time so this + * function has no effect. */ void time_refresh(void) { @@ -275,9 +289,17 @@ time_alarm(unsigned int secs) sigset_t oldsigs; time_init(); + block_sigalrm(&oldsigs); deadline = secs ? time_add(time_now(), secs) : TIME_MIN; unblock_sigalrm(&oldsigs); + + if (!CACHE_TIME) { + /* If we aren't timing the gaps between kernel time refreshes we need to + * to start the timer up now */ + set_up_signal(SA_RESTART); + set_up_timer(); + } } /* Like poll(), except: @@ -366,7 +388,7 @@ sigalrm_handler(int sig_nr) static void refresh_wall_if_ticked(void) { - if (wall_tick) { + if (!CACHE_TIME || wall_tick) { refresh_wall(); } } @@ -374,7 +396,7 @@ refresh_wall_if_ticked(void) static void refresh_monotonic_if_ticked(void) { - if (monotonic_tick) { + if (!CACHE_TIME || monotonic_tick) { refresh_monotonic(); } } diff --git a/lib/timeval.h b/lib/timeval.h index e8413ff2..1384848a 100644 --- a/lib/timeval.h +++ b/lib/timeval.h @@ -36,6 +36,21 @@ BUILD_ASSERT_DECL(TYPE_IS_INTEGER(time_t)); * ever encounter such a platform. */ BUILD_ASSERT_DECL(TYPE_IS_SIGNED(time_t)); +/* On x86-64 systems, Linux avoids using syscalls for clock_gettime(). + * + * For systems which do invoke a system call we wait at least + * TIME_UPDATE_INTERVAL ms between clock_gettime() calls and cache the time for + * the interim. + * + * For systems which do not invoke a system call, we just call clock_gettime() + * whenever the time is requested. As a result we don't start the background + * SIGALRM timer unless explicitly needed by time_alarm() */ +#if defined __x86_64__ && defined __linux__ +#define CACHE_TIME 0 +#else +#define CACHE_TIME 1 +#endif + #define TIME_MAX TYPE_MAXIMUM(time_t) #define TIME_MIN TYPE_MINIMUM(time_t) diff --git a/tests/test-timeval.c b/tests/test-timeval.c index d277fc96..9896cf73 100644 --- a/tests/test-timeval.c +++ b/tests/test-timeval.c @@ -97,6 +97,12 @@ main(int argc, char *argv[]) if (argc != 2) { usage(); } else if (!strcmp(argv[1], "plain")) { + /* If we're not caching time there isn't much to test and SIGALRM won't + * be around to pull us out of the select() call, so just skip out */ + if (!CACHE_TIME) { + exit (77); + } + do_test(); } else if (!strcmp(argv[1], "daemon")) { /* Test that time still advances even in a daemon. This is an @@ -104,6 +110,10 @@ main(int argc, char *argv[]) char cwd[1024], *pidfile; FILE *success; + if (!CACHE_TIME) { + exit (77); + } + assert(getcwd(cwd, sizeof cwd) == cwd); unlink("test-timeval.success");