Date: Mon, 9 Sep 2019 21:48:05 +0300 From: Konstantin Belousov <kostikbel@gmail.com> To: Conrad Meyer <cem@freebsd.org> Cc: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r352059 - head/sys/kern Message-ID: <20190909184805.GV2559@kib.kiev.ua> In-Reply-To: <CAG6CVpXyhxDc=D0ZWXoQeFPr6A3CrOK1MNeO7MVmjc4uVYTBvQ@mail.gmail.com> References: <201909091129.x89BTxvw061871@repo.freebsd.org> <CAG6CVpXyhxDc=D0ZWXoQeFPr6A3CrOK1MNeO7MVmjc4uVYTBvQ@mail.gmail.com>
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On Mon, Sep 09, 2019 at 11:31:32AM -0700, Conrad Meyer wrote: > What’s the motivation for using more timehands? See the thread titled 'Is it a good idea to use a usb-serial adapter for PPS input? Yes, it is.' on arm@ and usb@. In short, there are some reports of timecounters misbehaving on single-core systems when only two timehands are enabled. The change eases the experimentation and provides a workaround which does not require modifying the sources to apply. > > On Mon, Sep 9, 2019 at 04:30 Konstantin Belousov <kib@freebsd.org> wrote: > > > Author: kib > > Date: Mon Sep 9 11:29:58 2019 > > New Revision: 352059 > > URL: https://svnweb.freebsd.org/changeset/base/352059 > > > > Log: > > Make timehands count selectable at boottime. > > > > Tested by: O'Connor, Daniel <darius@dons.net.au> > > Sponsored by: The FreeBSD Foundation > > MFC after: 1 week > > Differential revision: https://reviews.freebsd.org/D21563 > > > > Modified: > > head/sys/kern/kern_tc.c > > > > Modified: head/sys/kern/kern_tc.c > > > > ============================================================================== > > --- head/sys/kern/kern_tc.c Mon Sep 9 11:22:38 2019 (r352058) > > +++ head/sys/kern/kern_tc.c Mon Sep 9 11:29:58 2019 (r352059) > > @@ -83,19 +83,16 @@ struct timehands { > > struct timehands *th_next; > > }; > > > > -static struct timehands th0; > > -static struct timehands th1 = { > > - .th_next = &th0 > > -}; > > -static struct timehands th0 = { > > +static struct timehands ths[16] = { > > + [0] = { > > .th_counter = &dummy_timecounter, > > .th_scale = (uint64_t)-1 / 1000000, > > .th_offset = { .sec = 1 }, > > .th_generation = 1, > > - .th_next = &th1 > > + }, > > }; > > > > -static struct timehands *volatile timehands = &th0; > > +static struct timehands *volatile timehands = &ths[0]; > > struct timecounter *timecounter = &dummy_timecounter; > > static struct timecounter *timecounters = &dummy_timecounter; > > > > @@ -115,6 +112,10 @@ static int timestepwarnings; > > SYSCTL_INT(_kern_timecounter, OID_AUTO, stepwarnings, CTLFLAG_RW, > > ×tepwarnings, 0, "Log time steps"); > > > > +static int timehands_count = 2; > > +SYSCTL_INT(_kern_timecounter, OID_AUTO, timehands_count, CTLFLAG_RDTUN, > > + &timehands_count, 0, "Count of timehands in rotation"); > > + > > struct bintime bt_timethreshold; > > struct bintime bt_tickthreshold; > > sbintime_t sbt_timethreshold; > > @@ -1960,8 +1961,9 @@ done: > > static void > > inittimecounter(void *dummy) > > { > > + struct timehands *thp; > > u_int p; > > - int tick_rate; > > + int i, tick_rate; > > > > /* > > * Set the initial timeout to > > @@ -1987,6 +1989,16 @@ inittimecounter(void *dummy) > > #ifdef FFCLOCK > > ffclock_init(); > > #endif > > + > > + /* Set up the requested number of timehands. */ > > + if (timehands_count < 1) > > + timehands_count = 1; > > + if (timehands_count > nitems(ths)) > > + timehands_count = nitems(ths); > > + for (i = 1, thp = &ths[0]; i < timehands_count; thp = &ths[i++]) > > + thp->th_next = &ths[i]; > > + thp->th_next = &ths[0]; > > + > > /* warm up new timecounter (again) and get rolling. */ > > (void)timecounter->tc_get_timecount(timecounter); > > (void)timecounter->tc_get_timecount(timecounter); > > > >
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