lkml.org 
[lkml]   [2018]   [Jul]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [RFC PATCH 1/2] time: Introduce one suspend clocksource to compensate the suspend time
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

\
 
 \ /
  Last update: 2018-07-16 11:09    [W:0.069 / U:0.108 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site