> -----Original Message----- > From: linux-rt-users-owner@xxxxxxxxxxxxxxx [mailto:linux-rt-users- > owner@xxxxxxxxxxxxxxx] On Behalf Of Luis Claudio R. Goncalves > Sent: Thursday, April 23, 2015 6:15 AM > To: Jiang, Yunhong > Cc: linux-rt-users@xxxxxxxxxxxxxxx > Subject: Re: Should I still use pm_timer as clock source for hrt mode > > On Tue, Apr 21, 2015 at 05:08:58PM +0000, Jiang, Yunhong wrote: > | Hi, all > | I noticed followed statement about TSC timer on > | https://rt.wiki.kernel.org/index.php/RT_PREEMPT_HOWTO , " Since the > TSC > | timer on PC platforms, as used in the previous versions, are now marked as > | unsuitable for hrt mode due to many lacks of functionalities and > | reliabilities, you will need i.E. pm_timer as provided by ACPI to use as > | clock source". > | > | I'm testing on Intel Xeon CPU E5-2640 and has "Switched to > | clocksource tsc" on kernel log, I think it mean the TSC on my system is > | stable and reliable enough to use as clock source, right? With the > | invariant and synchronized TSC support in latest hardware, can I assume > | generally TSC would be better than pm_timer? > > Nowadays the clocksourse selection code is a bit smarter than it was a > while ago. Some TSC clocks will be reliable as long as your system does not > enter deeper C-states, some will stop in idle... the kernel will select TSC > as the preferred clocksource and will use it until the event that could > render that specific TSC unreliable happens. Then the next better > clocksource option will be selected. > > And yes, reading the TSC is way faster and cheaper than reading pm_timer. > So, if TSC is available and is considered reliable, use the TSC. > > Depending on your environment and operation parameters you could take > some > extra steps to ensure the condition that would turn your TSC clock unreliable > never happens. E.g. avoid entering deeper C-states, booting with > idle=pool, ... > > Of course, any these changes have an effect, be it in power consumption or > processor temperature. Be sure to understand that balance and then decide > whether the cost of a lighter clock (in terms of cost to read the current > time) is more important than saving a few Watts on the end of day. > > Luis Thanks for your detailed reply and analysis. --jyh > -- > To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
