On 10/22/2021 1:58 PM, Keller, Jacob E wrote:
> The phc_ctl program includes an implementation for comparing the PHC
> with CLOCK_REALTIME when PTP_SYS_OFFSET ioctls are not supported.
>
> This implementation produces inverted results when compared with the
> implementation of the ioctl.
>
> The PTP_SYS_OFFSET ioctls calculate the difference as "CLOCK_REALTIME -
> PHC_TIME" while this function calculates "PHC_TIME - CLOCK_REALTIME".
> This could produce confusing results if phc_ctl is used on a kernel
> which lacks the PTP_SYS_OFFSET ioctls.
>
> Fix this by replacing the bespoke implementation in test_phc with the
> clockadj_compare function. That function mimics the interface of
> sysoff_measure and correctly computes the time offset between the two
> clocks in the same manner as the ioctls do. In addition, it supports
> performing multiple samples to reduce inaccuracy.
>
> With this change, the fallback implementation of measurement will match
> the behavior of the ioctl based PTP_SYS_OFFSET flows.
>
> Signed-off-by: Jacob Keller <[email protected]>
> ---
> phc_ctl.c | 54 ++++++++++++++++--------------------------------------
> 1 file changed, 16 insertions(+), 38 deletions(-)
>
> diff --git a/phc_ctl.c b/phc_ctl.c
> index 673cb37e3583..e975dd803578 100644
> --- a/phc_ctl.c
> +++ b/phc_ctl.c
> @@ -90,26 +90,6 @@ static int install_handler(int signum, void(*handler)(int))
> return 0;
> }
>
> -static int64_t calculate_offset(struct timespec *ts1,
> - struct timespec *rt,
> - struct timespec *ts2)
> -{
> - int64_t interval;
> - int64_t offset;
> -
> -#define NSEC_PER_SEC 1000000000ULL
> - /* calculate interval between clock realtime */
> - interval = (ts2->tv_sec - ts1->tv_sec) * NSEC_PER_SEC;
> - interval += ts2->tv_nsec - ts1->tv_nsec;
> -
> - /* assume PHC read occured half way between CLOCK_REALTIME reads */
> -
> - offset = (rt->tv_sec - ts1->tv_sec) * NSEC_PER_SEC;
> - offset += (rt->tv_nsec - ts1->tv_nsec) - (interval / 2);
> -
> - return offset;
> -}
> -
> static void usage(const char *progname)
> {
> fprintf(stderr,
> @@ -335,34 +315,32 @@ static int do_caps(clockid_t clkid, int cmdc, char
> *cmdv[])
>
> static int do_cmp(clockid_t clkid, int cmdc, char *cmdv[])
> {
> - struct timespec ts, rta, rtb;
> - int64_t sys_offset, delay = 0, offset;
> + int64_t sys_offset, delay;
> uint64_t sys_ts;
> - int method;
> + int method, fd;
>
> - method = sysoff_probe(CLOCKID_TO_FD(clkid), 9);
> +#define N_SAMPLES 9
>
> - if (method >= 0 && sysoff_measure(CLOCKID_TO_FD(clkid), method, 9,
> + fd = CLOCKID_TO_FD(clkid);
> +
> + method = sysoff_probe(fd, N_SAMPLES);
> +
> + if (method >= 0 && sysoff_measure(fd, method, N_SAMPLES,
> &sys_offset, &sys_ts, &delay) >= 0) {
> - pr_notice( "offset from CLOCK_REALTIME is %"PRId64"ns\n",
> - sys_offset);
> + pr_notice("offset from CLOCK_REALTIME is %"PRId64"ns\n",
> + sys_offset);
> return 0;
> }
>
> - memset(&ts, 0, sizeof(ts));
> - memset(&rta, 0, sizeof(rta));
> - memset(&rtb, 0, sizeof(rtb));
> - if (clock_gettime(CLOCK_REALTIME, &rta) ||
> - clock_gettime(clkid, &ts) ||
> - clock_gettime(CLOCK_REALTIME, &rtb)) {
> - pr_err("cmp: failed clock reads: %s\n",
> - strerror(errno));
> + if (clockadj_compare(clkid, CLOCK_REALTIME, N_SAMPLES,
> + &sys_offset, &sys_ts, &delay)) {
> + pr_err("cmp: failed to compare clocks: %s\n",
> + strerror(errno));
> return -1;
> }
Oops. This part is wrong. clockadj_compare returns positive when it
succeeds... Maybe that should be fixed to match expected functions...
Thanks,
Jake
>
> - offset = calculate_offset(&rta, &ts, &rtb);
> - pr_notice( "offset from CLOCK_REALTIME is approximately %"PRId64"ns\n",
> - offset);
> + pr_notice("offset from CLOCK_REALTIME is approximately %"PRId64"ns\n",
> + sys_offset);
>
> return 0;
> }
>
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