Hi Arne, > But that also > implies it is the other way round on other platforms. The update_time > function is > called in multiple critical places. Do we have any idea about this?
On Linux with glibc's implementation both time() and gettimeofday() results in the same clock_gettime() call over VDSO (https://man7.org/linux/man-pages/man7/vdso.7.html). On FreeBSD (and so), same if VDSO is used both time() and gettimeofday() will use clock_gettime too with even additional "tv->tv_usec = 0" for time(). So, on most of architectures there will be no difference after replacing time() to gettimeofday() except. asm commands for moving 32/64bit tv_usec, it'll be not visible. On some acrhs/systems where VDSO is not supported - same syscall will happen. > I remember > vaguely that the default gettimeofday in FreeBSD is more accurate than the > Linux variant (involves a kernel call) but you can request a version similar > to the > Linux one by some flag (reading from a shared readonly memory page that is > read only). As for clock drifting, it maybe feasible to use clock_gettime() with CLOCK_MONOTONIC and get rid of homegrown time adj code at all -> returned time will always be monotonic by design. At least on supported platforms (!_WIN32). -- Best Regards, Vladislav Grishenko > -----Original Message----- > From: Arne Schwabe <a...@rfc2549.org> > Sent: Tuesday, September 22, 2020 1:41 PM > To: Vladislav Grishenko <themi...@yandex-team.ru>; openvpn- > de...@lists.sourceforge.net > Subject: Re: [Openvpn-devel] [PATCH] Fix update_time() and > openvpn_gettimeofday() > > > > --- a/src/openvpn/otime.h > > +++ b/src/openvpn/otime.h > > @@ -78,13 +78,9 @@ openvpn_gettimeofday(struct timeval *tv, void *tz) > > static inline void > > update_time(void) > > { > > -#ifdef _WIN32 > > - /* on _WIN32, gettimeofday is faster than time(NULL) */ > > + /* can't use time(NULL), now_usec needs to be updated */ > > struct timeval tv; > > openvpn_gettimeofday(&tv, NULL); > > -#else > > - update_now(time(NULL)); > > -#endif > > } > > > > #else /* !TIME_BACKTRACK_PROTECTION */ > > > > I am hesitant about this change, it mentions that gettimeofday is faster on > Windows than time(NULL) and we prefer it there for this reason. But that also > implies it is the other way round on other platforms. The update_time > function is > called in multiple critical places. Do we have any idea about this? I remember > vaguely that the default gettimeofday in FreeBSD is more accurate than the > Linux variant (involves a kernel call) but you can request a version similar > to the > Linux one by some flag (reading from a shared readonly memory page that is > read only). > > Arne _______________________________________________ Openvpn-devel mailing list Openvpn-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/openvpn-devel
