Re: test jiffies on ARM SMP board
On 2013年02月21日 01:30, Russell King - ARM Linux wrote:
On Wed, Feb 20, 2013 at 10:54:41PM +0530, anish kumar wrote:
On Thu, 2013-02-21 at 00:39 +0800, buyitian wrote:
i am confused about my test. in one device driver,
i put below code:
printk(start to test test jiffies\n);
local_irq_save(flags);
jf1 = jiffies; // read jiffies first time
// hold cpu for about 2 seconds(do some calculation)
jf2 = jiffies; // read jiffies after 2 seconds
local_irq_restore(flags);
printk(jf1:%lu, jf2:%lu\n, jf1, jf2);
and the output is as below:
4[ 108.551124]start to test test jiffies
4[ 110.367604]jf1:4294948151, jf2:4294948151
the jf1 and jf2 are the same value, although they are
read between 2 seconds interval, i think this is because
i disabled local interrupt.
but the printk timestamp is from 108.551124 to 110.367604,
which is about 2 seconds. and on my platform, printk timestamp
is got from the function read_sched_clock:
static u32 __read_mostly (*read_sched_clock)(void) = jiffy_sched_clock_read;
and function jiffy_sched_clock_read() is to read from jiffies.
it seems that the jiffies is frozen when local irq is disabled,
but after local_irq_restore(), the jiffies not only start
to run, but also recover the lost 2 seconds.
is the jiffies updated from another cpu when irq is disabled on
local cpu?
is there some internel processor interrupt between cpu1 and cpu0
after local irq is re-enabled so that jiffies recover the lost 2 seconds?
I think it is because of the fact that some RTC registers keep the
The RTC has nothing to do with this.
As soon as the IRQs are allowed again (immediately after the
local_irq_restore()) the pending interrupt - including the timer
interrupt will be processed.
At this point, because we read the clocksource, we can see that two
seconds have passed, and so we advance jiffies by the elapsed time.
80 /*
81 * Event handler for periodic ticks
82 */
83 void tick_handle_periodic(struct clock_event_device *dev)
84 {
85 int cpu = smp_processor_id();
86 ktime_t next;
87
88 tick_periodic(cpu);
89
90 if (dev-mode != CLOCK_EVT_MODE_ONESHOT)
91 return;
92 /*
93 * Setup the next period for devices, which do not have
94 * periodic mode:
95 */
96 next = ktime_add(dev-next_event, tick_period);
97 for (;;) {
98 if (!clockevents_program_event(dev, next, ktime_get())) --- once
irq enabled, here we got -ETIME, then
99 return;
100 /*
101 * Have to be careful here. If we're in oneshot mode,
102 * before we call tick_periodic() in a loop, we need
103 * to be sure we're using a real hardware clocksource.
104 * Otherwise we could get trapped in an infinite
105 * loop, as the tick_periodic() increments jiffies,
106 * when then will increment time, posibly causing
107 * the loop to trigger again and again.
108 */
109 if (timekeeping_valid_for_hres())
110 tick_periodic(cpu);
here, we add missing jiffies
111 next = ktime_add(next, tick_period);
112 }
113 }
This means printk() sees that the two seconds have passed. But because
you're reading from jiffies within the interrupt disabled region, that
code can't see the missed ticks.
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Re: test jiffies on ARM SMP board
On Thu, 2013-02-21 at 00:39 +0800, buyitian wrote: i am confused about my test. in one device driver, i put below code: printk(start to test test jiffies\n); local_irq_save(flags); jf1 = jiffies; // read jiffies first time // hold cpu for about 2 seconds(do some calculation) jf2 = jiffies; // read jiffies after 2 seconds local_irq_restore(flags); printk(jf1:%lu, jf2:%lu\n, jf1, jf2); and the output is as below: 4[ 108.551124]start to test test jiffies 4[ 110.367604]jf1:4294948151, jf2:4294948151 the jf1 and jf2 are the same value, although they are read between 2 seconds interval, i think this is because i disabled local interrupt. but the printk timestamp is from 108.551124 to 110.367604, which is about 2 seconds. and on my platform, printk timestamp is got from the function read_sched_clock: static u32 __read_mostly (*read_sched_clock)(void) = jiffy_sched_clock_read; and function jiffy_sched_clock_read() is to read from jiffies. it seems that the jiffies is frozen when local irq is disabled, but after local_irq_restore(), the jiffies not only start to run, but also recover the lost 2 seconds. is the jiffies updated from another cpu when irq is disabled on local cpu? is there some internel processor interrupt between cpu1 and cpu0 after local irq is re-enabled so that jiffies recover the lost 2 seconds? I think it is because of the fact that some RTC registers keep the elapsed time and when the irq is re-enabled the kernel reads these registers to be in sync with time. However I am not that sure which registers as I think that depends on the RTC chip and chip changes based on different boards. I hope some expert on these matters can pitch in here. ___ Kernelnewbies mailing list kernelnewb...@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies -- To unsubscribe from this list: send the line unsubscribe linux-omap in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: test jiffies on ARM SMP board
On Wed, Feb 20, 2013 at 10:54:41PM +0530, anish kumar wrote: On Thu, 2013-02-21 at 00:39 +0800, buyitian wrote: i am confused about my test. in one device driver, i put below code: printk(start to test test jiffies\n); local_irq_save(flags); jf1 = jiffies; // read jiffies first time // hold cpu for about 2 seconds(do some calculation) jf2 = jiffies; // read jiffies after 2 seconds local_irq_restore(flags); printk(jf1:%lu, jf2:%lu\n, jf1, jf2); and the output is as below: 4[ 108.551124]start to test test jiffies 4[ 110.367604]jf1:4294948151, jf2:4294948151 the jf1 and jf2 are the same value, although they are read between 2 seconds interval, i think this is because i disabled local interrupt. but the printk timestamp is from 108.551124 to 110.367604, which is about 2 seconds. and on my platform, printk timestamp is got from the function read_sched_clock: static u32 __read_mostly (*read_sched_clock)(void) = jiffy_sched_clock_read; and function jiffy_sched_clock_read() is to read from jiffies. it seems that the jiffies is frozen when local irq is disabled, but after local_irq_restore(), the jiffies not only start to run, but also recover the lost 2 seconds. is the jiffies updated from another cpu when irq is disabled on local cpu? is there some internel processor interrupt between cpu1 and cpu0 after local irq is re-enabled so that jiffies recover the lost 2 seconds? I think it is because of the fact that some RTC registers keep the The RTC has nothing to do with this. As soon as the IRQs are allowed again (immediately after the local_irq_restore()) the pending interrupt - including the timer interrupt will be processed. At this point, because we read the clocksource, we can see that two seconds have passed, and so we advance jiffies by the elapsed time. This means printk() sees that the two seconds have passed. But because you're reading from jiffies within the interrupt disabled region, that code can't see the missed ticks. -- To unsubscribe from this list: send the line unsubscribe linux-omap in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: test jiffies on ARM SMP board
On Wed, 2013-02-20 at 17:30 +, Russell King - ARM Linux wrote: On Wed, Feb 20, 2013 at 10:54:41PM +0530, anish kumar wrote: On Thu, 2013-02-21 at 00:39 +0800, buyitian wrote: i am confused about my test. in one device driver, i put below code: printk(start to test test jiffies\n); local_irq_save(flags); jf1 = jiffies; // read jiffies first time // hold cpu for about 2 seconds(do some calculation) jf2 = jiffies; // read jiffies after 2 seconds local_irq_restore(flags); printk(jf1:%lu, jf2:%lu\n, jf1, jf2); and the output is as below: 4[ 108.551124]start to test test jiffies 4[ 110.367604]jf1:4294948151, jf2:4294948151 the jf1 and jf2 are the same value, although they are read between 2 seconds interval, i think this is because i disabled local interrupt. but the printk timestamp is from 108.551124 to 110.367604, which is about 2 seconds. and on my platform, printk timestamp is got from the function read_sched_clock: static u32 __read_mostly (*read_sched_clock)(void) = jiffy_sched_clock_read; and function jiffy_sched_clock_read() is to read from jiffies. it seems that the jiffies is frozen when local irq is disabled, but after local_irq_restore(), the jiffies not only start to run, but also recover the lost 2 seconds. is the jiffies updated from another cpu when irq is disabled on local cpu? is there some internel processor interrupt between cpu1 and cpu0 after local irq is re-enabled so that jiffies recover the lost 2 seconds? I think it is because of the fact that some RTC registers keep the The RTC has nothing to do with this. As soon as the IRQs are allowed again (immediately after the local_irq_restore()) the pending interrupt - including the timer interrupt will be processed. At this point, because we read the clocksource, we can see that two seconds have passed, and so we advance jiffies by the elapsed time. So I understand there is some register which stores the elapsed time and in my understanding it was RTC register which is wrong as suggested by you.I suppose some timer register is used for this information on the SOC. This means printk() sees that the two seconds have passed. But because you're reading from jiffies within the interrupt disabled region, that code can't see the missed ticks. -- To unsubscribe from this list: send the line unsubscribe linux-omap in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: test jiffies on ARM SMP board
On Wed, Feb 20, 2013 at 10:54 PM, anish kumar anish198519851...@gmail.com wrote: On Thu, 2013-02-21 at 00:39 +0800, buyitian wrote: i am confused about my test. in one device driver, i put below code: printk(start to test test jiffies\n); local_irq_save(flags); jf1 = jiffies; // read jiffies first time // hold cpu for about 2 seconds(do some calculation) jf2 = jiffies; // read jiffies after 2 seconds local_irq_restore(flags); printk(jf1:%lu, jf2:%lu\n, jf1, jf2); and the output is as below: 4[ 108.551124]start to test test jiffies 4[ 110.367604]jf1:4294948151, jf2:4294948151 the jf1 and jf2 are the same value, although they are read between 2 seconds interval, i think this is because i disabled local interrupt. but the printk timestamp is from 108.551124 to 110.367604, which is about 2 seconds. and on my platform, printk timestamp is got from the function read_sched_clock: static u32 __read_mostly (*read_sched_clock)(void) = jiffy_sched_clock_read; and function jiffy_sched_clock_read() is to read from jiffies. it seems that the jiffies is frozen when local irq is disabled, but after local_irq_restore(), the jiffies not only start to run, but also recover the lost 2 seconds. is the jiffies updated from another cpu when irq is disabled on local cpu? is there some internel processor interrupt between cpu1 and cpu0 after local irq is re-enabled so that jiffies recover the lost 2 seconds? I think it is because of the fact that some RTC registers keep the RTC (real time clock) chips are not very common in embedded SoCs. So I'm not sure if they are involved here. Eg: we work on multi-core media SoC and it doesn't have a RTC attached (if its needed it will have to be added as an external peripheral). The SoC does however have a couple of different clock sources for driving CPU, media decoder cores etc. HTH, -mandeep elapsed time and when the irq is re-enabled the kernel reads these registers to be in sync with time. However I am not that sure which registers as I think that depends on the RTC chip and chip changes based on different boards. I hope some expert on these matters can pitch in here. ___ Kernelnewbies mailing list kernelnewb...@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies ___ Kernelnewbies mailing list kernelnewb...@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies -- To unsubscribe from this list: send the line unsubscribe linux-omap in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
RE: test
-Original Message- From: linux-omap-ow...@vger.kernel.org [mailto:linux-omap- ow...@vger.kernel.org] On Behalf Of Aguirre Rodriguez, Sergio Alberto Sent: Thursday, March 19, 2009 4:51 PM To: linux-omap@vger.kernel.org Subject: test Aaah, Few folks hitting: Generating server: snip linux-omap@vger.kernel.org vger.kernel.org #vger.kernel.org #5.7.1 SMTP; 550 5.7.1 Content-Policy accept-into-freezer-1 msg: Bayes Statistical Bogofilter considers this message SPAM. BF:S 1 In case you disagree, send the ENTIRE message plus this error message to postmas...@vger.kernel.org ; S1758343AbZCRQ3X #SMTP# Anyone seen similar issues recently? Regards, Nishanth Menon -- To unsubscribe from this list: send the line unsubscribe linux-omap in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
