Date: Mon, 9 Sep 2019 12:14:19 -0700 From: Conrad Meyer <cem@freebsd.org> To: Konstantin Belousov <kostikbel@gmail.com> Cc: src-committers <src-committers@freebsd.org>, svn-src-all <svn-src-all@freebsd.org>, svn-src-head <svn-src-head@freebsd.org> Subject: Re: svn commit: r352059 - head/sys/kern Message-ID: <CAG6CVpX6wo4zNi-OEUjQvWZCZ9FsEV0%2BCXt3ggw_n%2BO9wPPC6w@mail.gmail.com> In-Reply-To: <20190909184805.GV2559@kib.kiev.ua> References: <201909091129.x89BTxvw061871@repo.freebsd.org> <CAG6CVpXyhxDc=D0ZWXoQeFPr6A3CrOK1MNeO7MVmjc4uVYTBvQ@mail.gmail.com> <20190909184805.GV2559@kib.kiev.ua>
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Thanks! On Mon, Sep 9, 2019 at 11:48 AM Konstantin Belousov <kostikbel@gmail.com> w= rote: > > On Mon, Sep 09, 2019 at 11:31:32AM -0700, Conrad Meyer wrote: > > What=E2=80=99s 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> wrot= e: > > > > > 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 > > > > > > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D > > > --- head/sys/kern/kern_tc.c Mon Sep 9 11:22:38 2019 (r352= 058) > > > +++ head/sys/kern/kern_tc.c Mon Sep 9 11:29:58 2019 (r352= 059) > > > @@ -83,19 +83,16 @@ struct timehands { > > > struct timehands *th_next; > > > }; > > > > > > -static struct timehands th0; > > > -static struct timehands th1 =3D { > > > - .th_next =3D &th0 > > > -}; > > > -static struct timehands th0 =3D { > > > +static struct timehands ths[16] =3D { > > > + [0] =3D { > > > .th_counter =3D &dummy_timecounter, > > > .th_scale =3D (uint64_t)-1 / 1000000, > > > .th_offset =3D { .sec =3D 1 }, > > > .th_generation =3D 1, > > > - .th_next =3D &th1 > > > + }, > > > }; > > > > > > -static struct timehands *volatile timehands =3D &th0; > > > +static struct timehands *volatile timehands =3D &ths[0]; > > > struct timecounter *timecounter =3D &dummy_timecounter; > > > static struct timecounter *timecounters =3D &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 =3D 2; > > > +SYSCTL_INT(_kern_timecounter, OID_AUTO, timehands_count, CTLFLAG_RDT= UN, > > > + &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 =3D 1; > > > + if (timehands_count > nitems(ths)) > > > + timehands_count =3D nitems(ths); > > > + for (i =3D 1, thp =3D &ths[0]; i < timehands_count; thp =3D = &ths[i++]) > > > + thp->th_next =3D &ths[i]; > > > + thp->th_next =3D &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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