From nobody Thu Oct 28 21:31:30 2021 X-Original-To: dev-commits-src-main@mlmmj.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mlmmj.nyi.freebsd.org (Postfix) with ESMTP id B80C9181B19C; Thu, 28 Oct 2021 21:31:30 +0000 (UTC) (envelope-from git@FreeBSD.org) Received: from mxrelay.nyi.freebsd.org (mxrelay.nyi.freebsd.org [IPv6:2610:1c1:1:606c::19:3]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256 client-signature RSA-PSS (4096 bits) client-digest SHA256) (Client CN "mxrelay.nyi.freebsd.org", Issuer "R3" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 4HgJfB4vz4z4clg; Thu, 28 Oct 2021 21:31:30 +0000 (UTC) (envelope-from git@FreeBSD.org) Received: from gitrepo.freebsd.org (gitrepo.freebsd.org [IPv6:2610:1c1:1:6068::e6a:5]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (Client did not present a certificate) by mxrelay.nyi.freebsd.org (Postfix) with ESMTPS id 887892F2B; Thu, 28 Oct 2021 21:31:30 +0000 (UTC) (envelope-from git@FreeBSD.org) Received: from gitrepo.freebsd.org ([127.0.1.44]) by gitrepo.freebsd.org (8.16.1/8.16.1) with ESMTP id 19SLVUgP093028; Thu, 28 Oct 2021 21:31:30 GMT (envelope-from git@gitrepo.freebsd.org) Received: (from git@localhost) by gitrepo.freebsd.org (8.16.1/8.16.1/Submit) id 19SLVUe8093027; Thu, 28 Oct 2021 21:31:30 GMT (envelope-from git) Date: Thu, 28 Oct 2021 21:31:30 GMT Message-Id: <202110282131.19SLVUe8093027@gitrepo.freebsd.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org From: Konstantin Belousov Subject: git: ae750fbac723 - main - kern_tc.c: Scaling/large delta recalculation List-Id: Commit messages for the main branch of the src repository List-Archive: https://lists.freebsd.org/archives/dev-commits-src-main List-Help: List-Post: List-Subscribe: List-Unsubscribe: Sender: owner-dev-commits-src-main@freebsd.org X-BeenThere: dev-commits-src-main@freebsd.org MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-Git-Committer: kib X-Git-Repository: src X-Git-Refname: refs/heads/main X-Git-Reftype: branch X-Git-Commit: ae750fbac72387c05c8e13623c2465b20497b4be Auto-Submitted: auto-generated X-ThisMailContainsUnwantedMimeParts: N The branch main has been updated by kib: URL: https://cgit.FreeBSD.org/src/commit/?id=ae750fbac72387c05c8e13623c2465b20497b4be commit ae750fbac72387c05c8e13623c2465b20497b4be Author: Sebastian Huber AuthorDate: 2021-10-28 08:22:58 +0000 Commit: Konstantin Belousov CommitDate: 2021-10-28 21:31:14 +0000 kern_tc.c: Scaling/large delta recalculation This change is a slight performance optimization for systems with a slow 64-bit division. The th->th_scale and th->th_large_delta values only depend on the timecounter frequency and the th->th_adjustment. The timecounter frequency of a timehand only changes when a new timecounter is activated for the timehand. The th->th_adjustment is only changed by the NTP second update. The NTP second update is not done for every call of tc_windup(). Move the code block to recalculate the scaling factor and the large delta of a timehand to the new helper function recalculate_scaling_factor_and_large_delta(). Call recalculate_scaling_factor_and_large_delta() when a new timecounter is activated and a NTP second update occurred. MFC after: 1 week --- sys/kern/kern_tc.c | 88 +++++++++++++++++++++++++++++++----------------------- 1 file changed, 50 insertions(+), 38 deletions(-) diff --git a/sys/kern/kern_tc.c b/sys/kern/kern_tc.c index 9a928ca37aff..f7bd116dabe2 100644 --- a/sys/kern/kern_tc.c +++ b/sys/kern/kern_tc.c @@ -1310,6 +1310,40 @@ tc_setclock(struct timespec *ts) } } +/* + * Recalculate the scaling factor. We want the number of 1/2^64 + * fractions of a second per period of the hardware counter, taking + * into account the th_adjustment factor which the NTP PLL/adjtime(2) + * processing provides us with. + * + * The th_adjustment is nanoseconds per second with 32 bit binary + * fraction and we want 64 bit binary fraction of second: + * + * x = a * 2^32 / 10^9 = a * 4.294967296 + * + * The range of th_adjustment is +/- 5000PPM so inside a 64bit int + * we can only multiply by about 850 without overflowing, that + * leaves no suitably precise fractions for multiply before divide. + * + * Divide before multiply with a fraction of 2199/512 results in a + * systematic undercompensation of 10PPM of th_adjustment. On a + * 5000PPM adjustment this is a 0.05PPM error. This is acceptable. + * + * We happily sacrifice the lowest of the 64 bits of our result + * to the goddess of code clarity. + */ +static void +recalculate_scaling_factor_and_large_delta(struct timehands *th) +{ + uint64_t scale; + + scale = (uint64_t)1 << 63; + scale += (th->th_adjustment / 1024) * 2199; + scale /= th->th_counter->tc_frequency; + th->th_scale = scale * 2; + th->th_large_delta = MIN(((uint64_t)1 << 63) / scale, UINT_MAX); +} + /* * Initialize the next struct timehands in the ring and make * it the active timehands. Along the way we might switch to a different @@ -1320,7 +1354,6 @@ tc_windup(struct bintime *new_boottimebin) { struct bintime bt; struct timehands *th, *tho; - uint64_t scale; u_int delta, ncount, ogen; int i; time_t t; @@ -1382,7 +1415,7 @@ tc_windup(struct bintime *new_boottimebin) tho->th_counter->tc_poll_pps(tho->th_counter); /* - * Deal with NTP second processing. The for loop normally + * Deal with NTP second processing. The loop normally * iterates at most once, but in extreme situations it might * keep NTP sane if timeouts are not run for several seconds. * At boot, the time step can be large when the TOD hardware @@ -1393,14 +1426,21 @@ tc_windup(struct bintime *new_boottimebin) bt = th->th_offset; bintime_add(&bt, &th->th_boottime); i = bt.sec - tho->th_microtime.tv_sec; - if (i > LARGE_STEP) - i = 2; - for (; i > 0; i--) { - t = bt.sec; - ntp_update_second(&th->th_adjustment, &bt.sec); - if (bt.sec != t) - th->th_boottime.sec += bt.sec - t; + if (i > 0) { + if (i > LARGE_STEP) + i = 2; + + do { + t = bt.sec; + ntp_update_second(&th->th_adjustment, &bt.sec); + if (bt.sec != t) + th->th_boottime.sec += bt.sec - t; + --i; + } while (i > 0); + + recalculate_scaling_factor_and_large_delta(th); } + /* Update the UTC timestamps used by the get*() functions. */ th->th_bintime = bt; bintime2timeval(&bt, &th->th_microtime); @@ -1418,40 +1458,12 @@ tc_windup(struct bintime *new_boottimebin) th->th_offset_count = ncount; tc_min_ticktock_freq = max(1, timecounter->tc_frequency / (((uint64_t)timecounter->tc_counter_mask + 1) / 3)); + recalculate_scaling_factor_and_large_delta(th); #ifdef FFCLOCK ffclock_change_tc(th); #endif } - /*- - * Recalculate the scaling factor. We want the number of 1/2^64 - * fractions of a second per period of the hardware counter, taking - * into account the th_adjustment factor which the NTP PLL/adjtime(2) - * processing provides us with. - * - * The th_adjustment is nanoseconds per second with 32 bit binary - * fraction and we want 64 bit binary fraction of second: - * - * x = a * 2^32 / 10^9 = a * 4.294967296 - * - * The range of th_adjustment is +/- 5000PPM so inside a 64bit int - * we can only multiply by about 850 without overflowing, that - * leaves no suitably precise fractions for multiply before divide. - * - * Divide before multiply with a fraction of 2199/512 results in a - * systematic undercompensation of 10PPM of th_adjustment. On a - * 5000PPM adjustment this is a 0.05PPM error. This is acceptable. - * - * We happily sacrifice the lowest of the 64 bits of our result - * to the goddess of code clarity. - * - */ - scale = (uint64_t)1 << 63; - scale += (th->th_adjustment / 1024) * 2199; - scale /= th->th_counter->tc_frequency; - th->th_scale = scale * 2; - th->th_large_delta = MIN(((uint64_t)1 << 63) / scale, UINT_MAX); - /* * Now that the struct timehands is again consistent, set the new * generation number, making sure to not make it zero.