| Message ID | 1421928077-4698-3-git-send-email-pang.xunlei@linaro.org |
|---|---|
| State | New |
| Headers | show |
Hi Thomas, On 23 January 2015 at 05:07, Thomas Gleixner <tglx@linutronix.de> wrote: > On Thu, 22 Jan 2015, Xunlei Pang wrote: >> When doing timekeeping_resume(), if the nonstop clocksource >> wraps back, "cycle_delta" will miss the wrap time. >> >> It's hard to determine the right CLOCKSOURCE_MASK(xxx) or >> something to add code for inspecting such behavior, and we >> don't have many existent nonstop clocksources, so just add >> a comment to indicate that if have this flag set, people >> are aware that this nonstop clocksource won't wrap back >> during system suspend/resume. > > -ENOPARSE > > What has the CLOCKSOURCE_MASK() to do with this and why is the fact > relevant, that we only have a few suspend_nonstop clock sources? Before this, I tried to add some code to catch such problem at the time of registering the clocksource, like using the CLOCKSOURCE_MASK(), for example 64bit counter will never wrap for us. But there may be other values like CLOCKSOURCE_MASK(56), I just can't figure out exactly how to do this judge. So, I think we can only add a comment to let the developer be aware of this when registering nonstop clocksource, that's what I want to express. > >> + >> +/* >> + * When setting this flag, you're also supposed to mean that it doesn't >> + * wrap back during system suspend/resume. See timekeeping_resume(). > > -ENOPARSE > > I guess what you want to say here is: > > /* > * clocksource continues to run during suspend and is guaranteed not to > * wrap around during long suspend periods. > */ > Yes, this description is way better :-) Thanks, Xunlei -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Hi Thomas, On 25 January 2015 at 01:07, Thomas Gleixner <tglx@linutronix.de> wrote: > On Sat, 24 Jan 2015, Xunlei Pang wrote: > >> Before this, I tried to add some code to catch such problem at the >> time of registering the clocksource, like using the >> CLOCKSOURCE_MASK(), for example 64bit counter will never wrap for >> us. But there may be other values like CLOCKSOURCE_MASK(56), I just >> can't figure out exactly how to do this judge. > > I don't think there is a good way to do so. Registration time is the > wrong place anyway because the problem depends on: > > - The width of the counter > - The frequency of the counter > > The frequency of the counter might even change after registration. Now > add the unknown duration of the suspend to the picture and you're > completely lost. > > All we can do is provide information about the actual wraparound time, > if the CLOCK_SOURCE_SUSPEND_NONSTOP flag is set and the wraparound > time is less than some reasonable margin. > Yes, we can only deal with it approximately. How about this? 1) Add a new member about reference wraparound time(max system suspend period allowed) to struct clocksource. In __clocksource_updatefreq_scale(), we can use "sec" which already applys 12.5% margin as its value. 2) Add a new tuneable sysctl threshold with a default time period value(for example, 365 days) We can also printk its value when booting or changing its value to notice people about this. 3) then, in timekeeping_resume(), we can compare the reference wraparound of the nonstop clocksource with the sysctl threshold to decide if it is dependable to use. Thanks, Xunlei > > > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h index abcafaa..8680189 100644 --- a/include/linux/clocksource.h +++ b/include/linux/clocksource.h @@ -207,6 +207,11 @@ struct clocksource { #define CLOCK_SOURCE_WATCHDOG 0x10 #define CLOCK_SOURCE_VALID_FOR_HRES 0x20 #define CLOCK_SOURCE_UNSTABLE 0x40 + +/* + * When setting this flag, you're also supposed to mean that it doesn't + * wrap back during system suspend/resume. See timekeeping_resume(). + */ #define CLOCK_SOURCE_SUSPEND_NONSTOP 0x80 #define CLOCK_SOURCE_RESELECT 0x100
When doing timekeeping_resume(), if the nonstop clocksource wraps back, "cycle_delta" will miss the wrap time. It's hard to determine the right CLOCKSOURCE_MASK(xxx) or something to add code for inspecting such behavior, and we don't have many existent nonstop clocksources, so just add a comment to indicate that if have this flag set, people are aware that this nonstop clocksource won't wrap back during system suspend/resume. Signed-off-by: Xunlei Pang <pang.xunlei@linaro.org> --- include/linux/clocksource.h | 5 +++++ 1 file changed, 5 insertions(+)