Messages in this thread | | | From | Baolin Wang <> | Date | Mon, 16 Jul 2018 17:09:13 +0800 | Subject | Re: [RFC PATCH 1/2] time: Introduce one suspend clocksource to compensate the suspend time |
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Hi Thomas,
On 16 July 2018 at 16:28, Thomas Gleixner <tglx@linutronix.de> wrote: > On Thu, 12 Jul 2018, Baolin Wang wrote: >> On some hardware with multiple clocksources, we have course grained >> clocksources that support the CLOCK_SOURCE_SUSPEND_NONSTOP flag, but >> which are less ideal for timekeeping then other clocksources which >> halt in suspend. >> >> Currently, the timekeeping core only supports timing suspend using >> CLOCK_SOURCE_SUSPEND_NONSTOP clocksources if that clocksource is the >> current clocksource for timekeeping. >> >> As a result, some architectures try to implement read_persisitent_clock64() >> using those non-stop clocksources, but isn't really ideal. Thus this >> patch provides logic to allow a registered SUSPEND_NONSTOP clocksource, > > Please see Documentation/process/submitting-patches.rst and search for > 'This patch...'
OK, I will try to improve the commit message.
> >> +/** >> + * clocksource_suspend_select - Select the best clocksource for suspend timing >> + * @fallback: if select a fallback clocksource >> + */ >> +static void clocksource_suspend_select(bool fallback) >> +{ >> + struct clocksource *cs, *old_suspend; >> + >> + old_suspend = suspend_clocksource; >> + if (fallback) >> + suspend_clocksource = NULL; >> + >> + list_for_each_entry(cs, &clocksource_list, list) { >> + /* Skip current if we were requested for a fallback. */ >> + if (fallback && cs == old_suspend) >> + continue; >> + >> + __clocksource_suspend_select(cs); >> + } >> + >> + /* If we failed to find a fallback restore the old one. */ >> + if (!suspend_clocksource) >> + suspend_clocksource = old_suspend; > > That's for the case where something tries to remove a clocksource, right?
Yes.
> The logic here looks odd as the calling code for the fallback case has to > check whether the clocksource which is about to be removed is the suspend > clocksource. Why not just returning -EBUSY/0 for the fallback case? > > The other question is whether this should be enforced. We might as well > decide to just let the clocksource go and have no suspend clocksource.
OK.
> >> +/** >> + * clocksource_start_suspend_timing - Start measuring the suspend timing >> + * @cs: current clocksource from timekeeping >> + * @start_cycles: current cycles from timekeeping >> + * >> + * This function will save the start cycle values of suspend timer to calculate >> + * the suspend time when resuming system. >> + * >> + * This function is called late in the suspend process from timekeeping_suspend(), >> + * that means processes are freezed, non-boot cpus and interrupts are disabled >> + * now. It is therefore possible to start the suspend timer without taking the >> + * clocksource mutex. >> + */ >> +void clocksource_start_suspend_timing(struct clocksource *cs, u64 start_cycles) >> +{ >> + if (!suspend_clocksource) >> + return; >> + >> + /* >> + * If current clocksource is the suspend timer, we should use the >> + * tkr_mono.cycle_last value as suspend_start to avoid same reading >> + * from suspend timer. >> + */ >> + if (clocksource_is_suspend(cs)) { >> + suspend_start = start_cycles; >> + return; >> + } >> + >> + if (suspend_clocksource->enable && >> + WARN_ON_ONCE(suspend_clocksource->enable(suspend_clocksource))) { >> + pr_warn_once("Failed to enable the non-suspend-able clocksource.\n"); >> + return; > > This is horrible to read and the WARN is really not helpful because > the bracktrace is already known.
Sure, will remove the WARN_ON_ONCE().
> >> @@ -779,6 +910,16 @@ int __clocksource_register_scale(struct clocksource *cs, u32 scale, u32 freq) >> { >> unsigned long flags; >> >> + /* >> + * The nonstop clocksource can be selected as the suspend clocksource to >> + * calculate the suspend time, so it should not supply suspend/resume >> + * interfaces to suspend the nonstop clocksource when system suspends. >> + */ >> + if ((cs->flags & CLOCK_SOURCE_SUSPEND_NONSTOP) && >> + (cs->suspend || cs->resume)) >> + pr_warn("Nonstop clocksource %s should not supply suspend/resume interfaces\n", >> + cs->name); > > Lacks braces. > > See https://lkml.kernel.org/r/alpine.DEB.2.20.1701171956290.3645@nanos
OK. I will add braces in next version. Thanks for your comments.
> > Othar that the few nits this looks good. Nice work! > > Thanks, > > tglx
-- Baolin Wang Best Regards
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