The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_ffclock.c

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    1 /*-
    2  * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
    3  *
    4  * Copyright (c) 2011 The University of Melbourne
    5  * All rights reserved.
    6  *
    7  * This software was developed by Julien Ridoux at the University of Melbourne
    8  * under sponsorship from the FreeBSD Foundation.
    9  *
   10  * Redistribution and use in source and binary forms, with or without
   11  * modification, are permitted provided that the following conditions
   12  * are met:
   13  * 1. Redistributions of source code must retain the above copyright
   14  *    notice, this list of conditions and the following disclaimer.
   15  * 2. Redistributions in binary form must reproduce the above copyright
   16  *    notice, this list of conditions and the following disclaimer in the
   17  *    documentation and/or other materials provided with the distribution.
   18  *
   19  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   20  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   21  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   22  * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   23  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   24  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   25  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   26  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   27  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   28  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   29  * SUCH DAMAGE.
   30  */
   31 
   32 #include <sys/cdefs.h>
   33 __FBSDID("$FreeBSD$");
   34 
   35 #include "opt_ffclock.h"
   36 
   37 #include <sys/param.h>
   38 #include <sys/bus.h>
   39 #include <sys/kernel.h>
   40 #include <sys/lock.h>
   41 #include <sys/module.h>
   42 #include <sys/mutex.h>
   43 #include <sys/priv.h>
   44 #include <sys/proc.h>
   45 #include <sys/sbuf.h>
   46 #include <sys/sysproto.h>
   47 #include <sys/sysctl.h>
   48 #include <sys/systm.h>
   49 #include <sys/timeffc.h>
   50 
   51 #ifdef FFCLOCK
   52 
   53 FEATURE(ffclock, "Feed-forward clock support");
   54 
   55 extern struct ffclock_estimate ffclock_estimate;
   56 extern struct bintime ffclock_boottime;
   57 extern int8_t ffclock_updated;
   58 extern struct mtx ffclock_mtx;
   59 
   60 /*
   61  * Feed-forward clock absolute time. This should be the preferred way to read
   62  * the feed-forward clock for "wall-clock" type time. The flags allow to compose
   63  * various flavours of absolute time (e.g. with or without leap seconds taken
   64  * into account). If valid pointers are provided, the ffcounter value and an
   65  * upper bound on clock error associated with the bintime are provided.
   66  * NOTE: use ffclock_convert_abs() to differ the conversion of a ffcounter value
   67  * read earlier.
   68  */
   69 void
   70 ffclock_abstime(ffcounter *ffcount, struct bintime *bt,
   71     struct bintime *error_bound, uint32_t flags)
   72 {
   73         struct ffclock_estimate cest;
   74         ffcounter ffc;
   75         ffcounter update_ffcount;
   76         ffcounter ffdelta_error;
   77 
   78         /* Get counter and corresponding time. */
   79         if ((flags & FFCLOCK_FAST) == FFCLOCK_FAST)
   80                 ffclock_last_tick(&ffc, bt, flags);
   81         else {
   82                 ffclock_read_counter(&ffc);
   83                 ffclock_convert_abs(ffc, bt, flags);
   84         }
   85 
   86         /* Current ffclock estimate, use update_ffcount as generation number. */
   87         do {
   88                 update_ffcount = ffclock_estimate.update_ffcount;
   89                 bcopy(&ffclock_estimate, &cest, sizeof(struct ffclock_estimate));
   90         } while (update_ffcount != ffclock_estimate.update_ffcount);
   91 
   92         /*
   93          * Leap second adjustment. Total as seen by synchronisation algorithm
   94          * since it started. cest.leapsec_next is the ffcounter prediction of
   95          * when the next leapsecond occurs.
   96          */
   97         if ((flags & FFCLOCK_LEAPSEC) == FFCLOCK_LEAPSEC) {
   98                 bt->sec -= cest.leapsec_total;
   99                 if (ffc > cest.leapsec_next)
  100                         bt->sec -= cest.leapsec;
  101         }
  102 
  103         /* Boot time adjustment, for uptime/monotonic clocks. */
  104         if ((flags & FFCLOCK_UPTIME) == FFCLOCK_UPTIME) {
  105                 bintime_sub(bt, &ffclock_boottime);
  106         }
  107 
  108         /* Compute error bound if a valid pointer has been passed. */
  109         if (error_bound) {
  110                 ffdelta_error = ffc - cest.update_ffcount;
  111                 ffclock_convert_diff(ffdelta_error, error_bound);
  112                 /* 18446744073709 = int(2^64/1e12), err_bound_rate in [ps/s] */
  113                 bintime_mul(error_bound, cest.errb_rate *
  114                     (uint64_t)18446744073709LL);
  115                 /* 18446744073 = int(2^64 / 1e9), since err_abs in [ns] */
  116                 bintime_addx(error_bound, cest.errb_abs *
  117                     (uint64_t)18446744073LL);
  118         }
  119 
  120         if (ffcount)
  121                 *ffcount = ffc;
  122 }
  123 
  124 /*
  125  * Feed-forward difference clock. This should be the preferred way to convert a
  126  * time interval in ffcounter values into a time interval in seconds. If a valid
  127  * pointer is passed, an upper bound on the error in computing the time interval
  128  * in seconds is provided.
  129  */
  130 void
  131 ffclock_difftime(ffcounter ffdelta, struct bintime *bt,
  132     struct bintime *error_bound)
  133 {
  134         ffcounter update_ffcount;
  135         uint32_t err_rate;
  136 
  137         ffclock_convert_diff(ffdelta, bt);
  138 
  139         if (error_bound) {
  140                 do {
  141                         update_ffcount = ffclock_estimate.update_ffcount;
  142                         err_rate = ffclock_estimate.errb_rate;
  143                 } while (update_ffcount != ffclock_estimate.update_ffcount);
  144 
  145                 ffclock_convert_diff(ffdelta, error_bound);
  146                 /* 18446744073709 = int(2^64/1e12), err_bound_rate in [ps/s] */
  147                 bintime_mul(error_bound, err_rate * (uint64_t)18446744073709LL);
  148         }
  149 }
  150 
  151 /*
  152  * Create a new kern.sysclock sysctl node, which will be home to some generic
  153  * sysclock configuration variables. Feed-forward clock specific variables will
  154  * live under the ffclock subnode.
  155  */
  156 
  157 SYSCTL_NODE(_kern, OID_AUTO, sysclock, CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
  158     "System clock related configuration");
  159 SYSCTL_NODE(_kern_sysclock, OID_AUTO, ffclock, CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
  160     "Feed-forward clock configuration");
  161 
  162 static char *sysclocks[] = {"feedback", "feed-forward"};
  163 #define MAX_SYSCLOCK_NAME_LEN 16
  164 #define NUM_SYSCLOCKS nitems(sysclocks)
  165 
  166 static int ffclock_version = 2;
  167 SYSCTL_INT(_kern_sysclock_ffclock, OID_AUTO, version, CTLFLAG_RD,
  168     &ffclock_version, 0, "Feed-forward clock kernel version");
  169 
  170 /* List available sysclocks. */
  171 static int
  172 sysctl_kern_sysclock_available(SYSCTL_HANDLER_ARGS)
  173 {
  174         struct sbuf *s;
  175         int clk, error;
  176 
  177         s = sbuf_new_for_sysctl(NULL, NULL,
  178             MAX_SYSCLOCK_NAME_LEN * NUM_SYSCLOCKS, req);
  179         if (s == NULL)
  180                 return (ENOMEM);
  181 
  182         for (clk = 0; clk < NUM_SYSCLOCKS; clk++) {
  183                 sbuf_cat(s, sysclocks[clk]);
  184                 if (clk + 1 < NUM_SYSCLOCKS)
  185                         sbuf_cat(s, " ");
  186         }
  187         error = sbuf_finish(s);
  188         sbuf_delete(s);
  189 
  190         return (error);
  191 }
  192 
  193 SYSCTL_PROC(_kern_sysclock, OID_AUTO, available,
  194     CTLTYPE_STRING | CTLFLAG_RD | CTLFLAG_NEEDGIANT, 0, 0,
  195     sysctl_kern_sysclock_available, "A",
  196     "List of available system clocks");
  197 
  198 /*
  199  * Return the name of the active system clock if read, or attempt to change
  200  * the active system clock to the user specified one if written to. The active
  201  * system clock is read when calling any of the [get]{bin,nano,micro}[up]time()
  202  * functions.
  203  */
  204 static int
  205 sysctl_kern_sysclock_active(SYSCTL_HANDLER_ARGS)
  206 {
  207         char newclock[MAX_SYSCLOCK_NAME_LEN];
  208         int error;
  209         int clk;
  210 
  211         /* Return the name of the current active sysclock. */
  212         strlcpy(newclock, sysclocks[sysclock_active], sizeof(newclock));
  213         error = sysctl_handle_string(oidp, newclock, sizeof(newclock), req);
  214 
  215         /* Check for error or no change */
  216         if (error != 0 || req->newptr == NULL)
  217                 goto done;
  218 
  219         /* Change the active sysclock to the user specified one: */
  220         error = EINVAL;
  221         for (clk = 0; clk < NUM_SYSCLOCKS; clk++) {
  222                 if (strncmp(newclock, sysclocks[clk],
  223                     MAX_SYSCLOCK_NAME_LEN - 1)) {
  224                         continue;
  225                 }
  226                 sysclock_active = clk;
  227                 error = 0;
  228                 break;
  229         }
  230 done:
  231         return (error);
  232 }
  233 
  234 SYSCTL_PROC(_kern_sysclock, OID_AUTO, active,
  235     CTLTYPE_STRING | CTLFLAG_RW | CTLFLAG_NEEDGIANT, 0, 0,
  236     sysctl_kern_sysclock_active, "A",
  237     "Name of the active system clock which is currently serving time");
  238 
  239 static int sysctl_kern_ffclock_ffcounter_bypass = 0;
  240 SYSCTL_INT(_kern_sysclock_ffclock, OID_AUTO, ffcounter_bypass, CTLFLAG_RW,
  241     &sysctl_kern_ffclock_ffcounter_bypass, 0,
  242     "Use reliable hardware timecounter as the feed-forward counter");
  243 
  244 /*
  245  * High level functions to access the Feed-Forward Clock.
  246  */
  247 void
  248 ffclock_bintime(struct bintime *bt)
  249 {
  250 
  251         ffclock_abstime(NULL, bt, NULL, FFCLOCK_LERP | FFCLOCK_LEAPSEC);
  252 }
  253 
  254 void
  255 ffclock_nanotime(struct timespec *tsp)
  256 {
  257         struct bintime bt;
  258 
  259         ffclock_abstime(NULL, &bt, NULL, FFCLOCK_LERP | FFCLOCK_LEAPSEC);
  260         bintime2timespec(&bt, tsp);
  261 }
  262 
  263 void
  264 ffclock_microtime(struct timeval *tvp)
  265 {
  266         struct bintime bt;
  267 
  268         ffclock_abstime(NULL, &bt, NULL, FFCLOCK_LERP | FFCLOCK_LEAPSEC);
  269         bintime2timeval(&bt, tvp);
  270 }
  271 
  272 void
  273 ffclock_getbintime(struct bintime *bt)
  274 {
  275 
  276         ffclock_abstime(NULL, bt, NULL,
  277             FFCLOCK_LERP | FFCLOCK_LEAPSEC | FFCLOCK_FAST);
  278 }
  279 
  280 void
  281 ffclock_getnanotime(struct timespec *tsp)
  282 {
  283         struct bintime bt;
  284 
  285         ffclock_abstime(NULL, &bt, NULL,
  286             FFCLOCK_LERP | FFCLOCK_LEAPSEC | FFCLOCK_FAST);
  287         bintime2timespec(&bt, tsp);
  288 }
  289 
  290 void
  291 ffclock_getmicrotime(struct timeval *tvp)
  292 {
  293         struct bintime bt;
  294 
  295         ffclock_abstime(NULL, &bt, NULL,
  296             FFCLOCK_LERP | FFCLOCK_LEAPSEC | FFCLOCK_FAST);
  297         bintime2timeval(&bt, tvp);
  298 }
  299 
  300 void
  301 ffclock_binuptime(struct bintime *bt)
  302 {
  303 
  304         ffclock_abstime(NULL, bt, NULL, FFCLOCK_LERP | FFCLOCK_UPTIME);
  305 }
  306 
  307 void
  308 ffclock_nanouptime(struct timespec *tsp)
  309 {
  310         struct bintime bt;
  311 
  312         ffclock_abstime(NULL, &bt, NULL, FFCLOCK_LERP | FFCLOCK_UPTIME);
  313         bintime2timespec(&bt, tsp);
  314 }
  315 
  316 void
  317 ffclock_microuptime(struct timeval *tvp)
  318 {
  319         struct bintime bt;
  320 
  321         ffclock_abstime(NULL, &bt, NULL, FFCLOCK_LERP | FFCLOCK_UPTIME);
  322         bintime2timeval(&bt, tvp);
  323 }
  324 
  325 void
  326 ffclock_getbinuptime(struct bintime *bt)
  327 {
  328 
  329         ffclock_abstime(NULL, bt, NULL,
  330             FFCLOCK_LERP | FFCLOCK_UPTIME | FFCLOCK_FAST);
  331 }
  332 
  333 void
  334 ffclock_getnanouptime(struct timespec *tsp)
  335 {
  336         struct bintime bt;
  337 
  338         ffclock_abstime(NULL, &bt, NULL,
  339             FFCLOCK_LERP | FFCLOCK_UPTIME | FFCLOCK_FAST);
  340         bintime2timespec(&bt, tsp);
  341 }
  342 
  343 void
  344 ffclock_getmicrouptime(struct timeval *tvp)
  345 {
  346         struct bintime bt;
  347 
  348         ffclock_abstime(NULL, &bt, NULL,
  349             FFCLOCK_LERP | FFCLOCK_UPTIME | FFCLOCK_FAST);
  350         bintime2timeval(&bt, tvp);
  351 }
  352 
  353 void
  354 ffclock_bindifftime(ffcounter ffdelta, struct bintime *bt)
  355 {
  356 
  357         ffclock_difftime(ffdelta, bt, NULL);
  358 }
  359 
  360 void
  361 ffclock_nanodifftime(ffcounter ffdelta, struct timespec *tsp)
  362 {
  363         struct bintime bt;
  364 
  365         ffclock_difftime(ffdelta, &bt, NULL);
  366         bintime2timespec(&bt, tsp);
  367 }
  368 
  369 void
  370 ffclock_microdifftime(ffcounter ffdelta, struct timeval *tvp)
  371 {
  372         struct bintime bt;
  373 
  374         ffclock_difftime(ffdelta, &bt, NULL);
  375         bintime2timeval(&bt, tvp);
  376 }
  377 
  378 /*
  379  * System call allowing userland applications to retrieve the current value of
  380  * the Feed-Forward Clock counter.
  381  */
  382 #ifndef _SYS_SYSPROTO_H_
  383 struct ffclock_getcounter_args {
  384         ffcounter *ffcount;
  385 };
  386 #endif
  387 /* ARGSUSED */
  388 int
  389 sys_ffclock_getcounter(struct thread *td, struct ffclock_getcounter_args *uap)
  390 {
  391         ffcounter ffcount;
  392         int error;
  393 
  394         ffcount = 0;
  395         ffclock_read_counter(&ffcount);
  396         if (ffcount == 0)
  397                 return (EAGAIN);
  398         error = copyout(&ffcount, uap->ffcount, sizeof(ffcounter));
  399 
  400         return (error);
  401 }
  402 
  403 /*
  404  * System call allowing the synchronisation daemon to push new feed-forward clock
  405  * estimates to the kernel. Acquire ffclock_mtx to prevent concurrent updates
  406  * and ensure data consistency.
  407  * NOTE: ffclock_updated signals the fftimehands that new estimates are
  408  * available. The updated estimates are picked up by the fftimehands on next
  409  * tick, which could take as long as 1/hz seconds (if ticks are not missed).
  410  */
  411 #ifndef _SYS_SYSPROTO_H_
  412 struct ffclock_setestimate_args {
  413         struct ffclock_estimate *cest;
  414 };
  415 #endif
  416 /* ARGSUSED */
  417 int
  418 sys_ffclock_setestimate(struct thread *td, struct ffclock_setestimate_args *uap)
  419 {
  420         struct ffclock_estimate cest;
  421         int error;
  422 
  423         /* Reuse of PRIV_CLOCK_SETTIME. */
  424         if ((error = priv_check(td, PRIV_CLOCK_SETTIME)) != 0)
  425                 return (error);
  426 
  427         if ((error = copyin(uap->cest, &cest, sizeof(struct ffclock_estimate)))
  428             != 0)
  429                 return (error);
  430 
  431         mtx_lock(&ffclock_mtx);
  432         memcpy(&ffclock_estimate, &cest, sizeof(struct ffclock_estimate));
  433         ffclock_updated++;
  434         mtx_unlock(&ffclock_mtx);
  435         return (error);
  436 }
  437 
  438 /*
  439  * System call allowing userland applications to retrieve the clock estimates
  440  * stored within the kernel. It is useful to kickstart the synchronisation
  441  * daemon with the kernel's knowledge of hardware timecounter.
  442  */
  443 #ifndef _SYS_SYSPROTO_H_
  444 struct ffclock_getestimate_args {
  445         struct ffclock_estimate *cest;
  446 };
  447 #endif
  448 /* ARGSUSED */
  449 int
  450 sys_ffclock_getestimate(struct thread *td, struct ffclock_getestimate_args *uap)
  451 {
  452         struct ffclock_estimate cest;
  453         int error;
  454 
  455         mtx_lock(&ffclock_mtx);
  456         memcpy(&cest, &ffclock_estimate, sizeof(struct ffclock_estimate));
  457         mtx_unlock(&ffclock_mtx);
  458         error = copyout(&cest, uap->cest, sizeof(struct ffclock_estimate));
  459         return (error);
  460 }
  461 
  462 #else /* !FFCLOCK */
  463 
  464 int
  465 sys_ffclock_getcounter(struct thread *td, struct ffclock_getcounter_args *uap)
  466 {
  467 
  468         return (ENOSYS);
  469 }
  470 
  471 int
  472 sys_ffclock_setestimate(struct thread *td, struct ffclock_setestimate_args *uap)
  473 {
  474 
  475         return (ENOSYS);
  476 }
  477 
  478 int
  479 sys_ffclock_getestimate(struct thread *td, struct ffclock_getestimate_args *uap)
  480 {
  481 
  482         return (ENOSYS);
  483 }
  484 
  485 #endif /* FFCLOCK */

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