I wrote a program for a LED display. The program allows to set the refresh rate via webconfiguration. To meet the refresh rate I measure the processing time of a loop. At the end I calculate the delay and wait until the next loop.
e.g. Refresh Rate 5 Hz -> 200 milli seconds for one loop. 50 milli seconds computing time results in 150 milli seconds delay.
The ratio of process time (50 milli seconds) to total time (200 milli seconds) indicates the processor load of my program. But to find the optimal setting, I need the actual total processor load. And not only that of my program. But since I don't know the real processor load of the delay() (in which WIFI etc. is done), I don't really know the processor load. In other words, I don't know how much time the system spends doing system tasks in the delay(150).
Is there a way to find out how much of a delay is actually used for system tasks before the processor truly waits?
In other words, I'm looking for a way to get the kernel time within a certain time frame.
Cheers Gabriel
Related
I am looking for a solution because the sth-channel is full.
I am troubled with calculating the appropriate capacity of channel capacity.
This document has the following description.
In order to calculate the appropriate capacity, just have in consideration the following parameters:
・The amount of events to be put into the channel by the sources per unit time (let's say 1 minute).
・The amount of events to be gotten from the channel by the sinks per unit time.
・An estimation of the amount of events that could not be processed per unit time, and thus to be reinjected into the channel (see next section).
How can I check the values of these parameters?
How can I check the values of these parameters?
You can't just check these parameters. They depend on your application.
What they are saying is that you should have a size which is large enough so the generator doesn't get stuck. This may not be possible in your application.
Say your generator receives one event per second and it takes 2 seconds for a receiver to manage that event. Now lets assume you have 3 receivers. In 1 second, you can manage to process 0.5 events per receiver. You have 3 receivers, so your receivers, together, are capable of processing 0.5 × 3 = 1.5 events, which is more than what you get as input. Your capacity can be 1 or 2, using 2 will greatly increase your chances that you do not get blocked.
Let's review another example:
Your generator wants to pushes 1,000 events per second
Your receivers take 3 seconds to process one event
You would need 1,000 x 3 = 3,000 receivers (3,000 goroutines that can run at full speed in parallel...)
In this example, the total number of receivers is so large that you have to either break up your code to work on multiple computers or optimize your receiver code so it can process the data in an amount of time that makes sense. Say you have 50 processors, your receivers will get 1,000 events per second, all 50 can run at full speed, you need one receiver to do its work in:
50 / 1000 = 0.05 seconds
Now let's assume that in most cases your goroutines take 0.02 but once in a while one will take 1 second. That means your goroutines can get a little behind. In that case your capacity (so the generator doesn't get blocked) should be a little over 1,000. Again, it will depend on how many of the routines get slowed down, etc. In this last example, a run is 0.02 seconds so to process 1,000 events it usually takes 0.02 seconds. If you can send those 1,000 event over the 1 second period, you may not even need the 50 goroutines and could have a smaller capacity. On the other hand, if you have big bursts where you may end up sending many (say 500) events all at ones, then more goroutines and a larger capacity is important to not get blocked.
If you are writing a bosun alert which is based of a percentage error rate for requests handled by your system, how do you write it in such a way that it handles periods of low traffic.
For example:
If I have an alert which looks back over the last 5 minutes and works out the error rate for requests
$errorRate = $numberErr/$numberReq and then triggers an alarm if the errorRate exceeds a predefined threshold crit = $errorRate > 0.05 this can work quite well so long as every 5 minute period had a sufficiently large number of requests ($numberReq).
If the number of requests in a 5 minute period was 10,000 then 501 errors would be required to trigger an alarm. However if the number of requests in a 5 minute period was 100 then only 5 errors would be required to trigger an alarm.
How can I write an alert which handles periods where the number of requests are so low that a small number of errors will equate to a large error rate. I had considered a sliding window of time, rather than a fixed 5 minute period, where the window would increase in size until the number of requests was high enough to give some confidence in the alarm. e.g. increase the time period until the number of requests is 10,000.
I can't find a way to achieve this in bosun, and I don't want to commit to a larger period of time for my alerts because the traffic rate varies so much. A longer period during peak traffic could result in an actual error causing a much larger impact.
I generally pair any percentage and/or historical based alerts with a static threshold.
For example: crit = numberErr > 100 && $errorRate > 0.05. That way the percent part doesn't matter unless the number of errors have also crossed some threshold because the entire statement won't be true.
I am trying to calculate the Read/second and Write/Second in my Cassandra 2.1 cluster. After searching and reading, I came to know about JMX bean
org.apache.cassandra.metrics:type=ClientRequest,scope=Write,name=Latency
Here I can see oneMinuteRate. I have started a brand new cluster and started collected these metrics from 0.
When I started my first record, I can see
Count = 1
OneMinuteRate = 0.01599111...
Does it mean that my write/s is 0.0159911?
Or does it mean that based on 1 minute data, my write latency is 0.01599 where Write Latency refers to the response time for writing a record?
Please help me understand the value.
Thanks.
It means that in the last minute, your writes per second were occuring at a rate of .01599 writes per second. Think about it this way: the rate of writes in the last 60 seconds would be
WritesInLastMinute ÷ 60
So in your case
1 ÷ 60 = 0.0166
Or more precisely, .01599.
If you observed no further writes after that, the value would descend down to zero over the next minute.
OneMinuteRate, FiveMinuteRate, and FifteenMinuteRate are exponential moving averages, meaning they are not simply dividing readings against time, instead, as the name implies they take an exponential series of averages as below:
result(t) = (1 - w) * result(t - 1) + (w) * event_this_period
where w is the weighting factor, t is the ticking time, in other words, simply they take 20% or the new reading and 80% of old readings, it's the same way UNIX systems measure CPU loads.
however, if this applies to requests that the server receives, below is a chart from one request to a server, measures taken by dropwizard.
as you can see, from one request a curve is drawn by time, it's really useful to determine trends, but not sure if they are great to monitor live traffic and especially critical one.
I need to calculate power consumption of CPU. According to this formula.
Power(mW) = cpu * 1.8 / time.
Where time is the sum of cpu + lpm.
I need to measure at the start of certain process and at the end, however the time passed it is to short, and cpu don't change to lpm mode as seen in the next values taken with powertrace_print().
all_cpu all_lpm all_transmit all_listen
116443 1514881 148 1531616
17268 1514881 148 1532440
Calculating power consumption of cpu I got 1.8 mW (which is exactly the value of current draw of CPU in active mode).
My question is, how calculate power consumption in this case?
If MCU does not go into a LPM, then it spends all the time in active mode, so the result of 1.8 mW you get looks correct.
Perhaps you want to ask something different? If you want to measure the time required to execute a specific block of code, you can add RTIMER_NOW() calls at the start and end of the block.
The time resolution of RTIMER_NOW may be too coarse for short-time operations. You can use a higher frequency timer for that, depending on your platform, e.g. read the TBR register for timing if you're compiling for a msp430 based sensor node.
I have to display a timer in 10th second for a sport competition. I have do this using the OnTimer event of a TTimer. the interval is set to 100. My routine display the current min:sec.10th (ex.: 02:45.7 ) correctly but it seem that my timer loose about 4 second at each minutes if I comp. to normal clock.
There is a better way to get a time accuracy timer in Delphi XE2 (or XE3) ?
You can use a timer to display the current value of the clock, but use a different approach to calculate the elapsed time.
You have to know that Windows timers are not time accurate, and even if you set it to elapse every 100 milliseconds, it can take more to fire the OnTimer event and even it can miss some intervals if for some reason elapses two or more times before your application process it.
You can, for example, use the system high-resolution performance counter to track times with nano-second accuracy.
You can also use the Delphi TStopwatch class, which encapsulates the system calls and falls back to other method (GetTickCount) if the high resolution performance counter is not available in your machine.
Take also a look at the How to Accurately Measure Elapsed Time Using High-Resolution Performance Counter delphi.about.com article.