On 16/12/20(Wed) 12:50, Scott Cheloha wrote:
> On Tue, Dec 15, 2020 at 01:47:24PM +0100, Mark Kettenis wrote:
> > > Date: Tue, 15 Dec 2020 13:32:22 +0100
> > > From: Claudio Jeker <cje...@diehard.n-r-g.com>
> > >
> > > On Fri, Dec 11, 2020 at 07:07:56PM -0600, Scott Cheloha wrote:
> > > > Hi,
> > > >
> > > > I'd like to remove lbolt from the kernel. I think having it in the
> > > > kernel complicates otherwise simple code.
> > > >
> > > > We can start with sdmmc(4).
> > > >
> > > > The goal in sdmmc_io_function_enable() is calling
> > > > sdmmc_io_function_ready()
> > > > up to six times and sleep 1 second between each attempt. Here's
> > > > rewritten
> > > > code that does with without lbolt.
> > > >
> > > > ok?
> > > >
> > > > Index: sdmmc_io.c
> > > > ===================================================================
> > > > RCS file: /cvs/src/sys/dev/sdmmc/sdmmc_io.c,v
> > > > retrieving revision 1.41
> > > > diff -u -p -r1.41 sdmmc_io.c
> > > > --- sdmmc_io.c 31 Dec 2019 10:05:33 -0000 1.41
> > > > +++ sdmmc_io.c 12 Dec 2020 01:04:59 -0000
> > > > @@ -231,8 +231,8 @@ sdmmc_io_function_enable(struct sdmmc_fu
> > > > {
> > > > struct sdmmc_softc *sc = sf->sc;
> > > > struct sdmmc_function *sf0 = sc->sc_fn0;
> > > > + int chan, retry = 5;
> > > > u_int8_t rv;
> > > > - int retry = 5;
> > > >
> > > > rw_assert_wrlock(&sc->sc_lock);
> > > >
> > > > @@ -244,7 +244,7 @@ sdmmc_io_function_enable(struct sdmmc_fu
> > > > sdmmc_io_write_1(sf0, SD_IO_CCCR_FN_ENABLE, rv);
> > > >
> > > > while (!sdmmc_io_function_ready(sf) && retry-- > 0)
> > > > - tsleep_nsec(&lbolt, PPAUSE, "pause", INFSLP);
> > > > + tsleep_nsec(&chan, PPAUSE, "pause", SEC_TO_NSEC(1));
> > > > return (retry >= 0) ? 0 : ETIMEDOUT;
> > > > }
> > > >
> > >
> > > Why not use &retry as wait channel instead of adding a new variable
> > > chan? Result is the same. Would it make sense to allow NULL as wait
> > > channel to make the tsleep not wakeable. At least that could be used in a
> > > few places where timeouts are implemented with tsleep and would make the
> > > intent more obvious.
> >
> > Or have an appropriately named global variable? Something like "int
> > nowake"?
>
> Something like the attached patch?
>
> I think the idea of a "dead channel" communicates the intent. Nobody
> broadcasts wakeups on the dead channel. If you don't want to receive
> wakeup broadcasts you sleep on the dead channel. Hence, "deadchan".
Why did we choose to use a variable over NULL? Any technical reason?
I'm wondering it the locality of the variable might not matter in a
distant future. Did you dig a bit deeper about the FreeBSD solution?
Why did they choose a per-CPU value?
> Index: kern/kern_synch.c
> ===================================================================
> RCS file: /cvs/src/sys/kern/kern_synch.c,v
> retrieving revision 1.172
> diff -u -p -r1.172 kern_synch.c
> --- kern/kern_synch.c 7 Dec 2020 16:55:29 -0000 1.172
> +++ kern/kern_synch.c 16 Dec 2020 18:50:12 -0000
> @@ -87,6 +87,12 @@ sleep_queue_init(void)
> TAILQ_INIT(&slpque[i]);
> }
>
> +/*
> + * Threads that do not want to receive wakeup(9) broadcasts should
> + * sleep on deadchan.
> + */
> +static int __deadchan;
> +int *deadchan = &__deadchan;
>
> /*
> * During autoconfiguration or after a panic, a sleep will simply
> Index: sys/systm.h
> ===================================================================
> RCS file: /cvs/src/sys/sys/systm.h,v
> retrieving revision 1.148
> diff -u -p -r1.148 systm.h
> --- sys/systm.h 26 Aug 2020 03:29:07 -0000 1.148
> +++ sys/systm.h 16 Dec 2020 18:50:12 -0000
> @@ -107,6 +107,8 @@ extern struct vnode *rootvp; /* vnode eq
> extern dev_t swapdev; /* swapping device */
> extern struct vnode *swapdev_vp;/* vnode equivalent to above */
>
> +extern int *deadchan; /* dead wakeup(9) channel */
> +
> struct proc;
> struct process;
> #define curproc curcpu()->ci_curproc
> Index: dev/sdmmc/sdmmc_io.c
> ===================================================================
> RCS file: /cvs/src/sys/dev/sdmmc/sdmmc_io.c,v
> retrieving revision 1.41
> diff -u -p -r1.41 sdmmc_io.c
> --- dev/sdmmc/sdmmc_io.c 31 Dec 2019 10:05:33 -0000 1.41
> +++ dev/sdmmc/sdmmc_io.c 16 Dec 2020 18:50:12 -0000
> @@ -244,7 +244,7 @@ sdmmc_io_function_enable(struct sdmmc_fu
> sdmmc_io_write_1(sf0, SD_IO_CCCR_FN_ENABLE, rv);
>
> while (!sdmmc_io_function_ready(sf) && retry-- > 0)
> - tsleep_nsec(&lbolt, PPAUSE, "pause", INFSLP);
> + tsleep_nsec(deadchan, PPAUSE, "pause", SEC_TO_NSEC(1));
> return (retry >= 0) ? 0 : ETIMEDOUT;
> }
>
>
