I would like to know if it is possible to modify easily perf linux with stat module to create an interval of cycles (or instructions by cycle) instead of an interval of time ? The goal is to optimize the precision of the counters got by interval. The time unit is not accurate enough.
I have a friend which submits this idea but I looked the source code a little and I understood (maybe I have wrong) that we :
create a condition for a time calculated with the rdtsc library (some clock_gettime)
create a "wait" in the perf processus
launch the program to test
test if we respect the time condition : we continue or we break the wait function with a save on the mapped register system information in perf (and call the wait function if it is not over)
I would like this result :
cycles counts unit events
10000 25000 instructions
10000 450 branch-misses
20000 21000 instructions
20000 850 branch-misses
Unfortunately, I'm seeing a big problem if I want to use the result of a counter like a condition I have not yet. Or should I get all the time this or these counter(s) which define my "interval condition" ? I also saw that for a time interval, we shouldn't get counters with a frequency lower than 100ms because it generates overhead. If I get some counters every 10000 cycles, would I have the same problems ? I don't know where is this overhead (calls system ?).
I am working on my graduation project. It is a digital protection relay which trips if the measured value exceeds a specific value. It must trip after a time delay. We use texas instrument kit and simulink to build the program.
My problem is how to make a time delay so that i can delay the trip signal with predetermined time. The attached image shows aport of the program
thanks.
You can implement that by creating a counter (integrator). For example the counter increments (counter_value +=.001) by one each millisecond. Your trip delay is 1.54 s then you compare (>=) the value of the counter to your trip delay.
The counter is activated and reset by the boolean input signal that you want to delay.
I dont have Simulink installed. Therefore i cant give you a picture, and i think pseudocode would not help much either.
Is there some type of conversion for ticks to a unit of real time? I would like my program to simulate a 48 hour experiment. Does anyone have any suggestions on how to do this? Thanks!
How quickly do things change in your experiment? From system dynamics, a good rule of thumb is to have a discrete clock tick 4 times during the smallest interval of real time in which something meaningful happens in the modelled system. For example, if you would expect to see changes every minute, then you would have 4 ticks each minute (and your ABM rules about updating the system would be calculated on the basis of 15 seconds) and then run the simulation for 11,520 (=48x60x4) ticks.
I need to calculate the cpu usage and aggregate it from proc file in linux
/proc/stat gives me data but how would i come to know the % used of cpu at time as
stat gives me the count of processes at cores running at any time which does not give me any idea of %use of cpu?
And i am coding this in Golang and have to do this w/o scripts
Thanks in advance!!
/proc/stat does not only give you the count of processes on each core. man proc will tell you the exact format of that file. Copied from it, here is the part you should be interested in:
/proc/stat
cpu 3357 0 4313 1362393
The amount of time, measured in units of USER_HZ
(1/100ths of a second on most architectures, use
sysconf(_SC_CLK_TCK) to obtain the right value), that the
system spent in user mode, user mode with low priority
(nice), system mode, and the idle task, respectively.
The last value should be USER_HZ times the second entry
in the uptime pseudo-file.
It is then easy to do the substraction of the idle field between two measures, which will give you the time spent not doing anything by this CPU. The other value that you can extract is the time doing something, which is the difference between two measures of:
time in user mode + time spent in user mode with low priority + time spent in system mode
You will then have two values; one, A, is expressing the time doing nothing, and the other, B, the time actually doing something. B / (A + B) will give you the percentage of time the CPU was busy.
I have a very hard problem:
I have round about 20-50 objects, which I MUST (that is given for the problem, please don't spend time in thinking around it) put througt a logic EVERY SECOND.
The logic itself need round about 200-600 milliseconds (90% it is 200ms - 10% it is 600ms).
I try to find any solution how I can make is smaller, but there isn't. I must get an object from DB, I must have a lot of if-else and I must actual it. - Even if I reduce it to 50ms or smaller, to veriable rate of the object up to 50 will break my neck with the 1 second timer, because 50 x 50mx =2,5 second. So a tick needs longer then the tickrate should be.
So, my only, not very smart I think, idea is to open for every object an own thread and lead a mainthread for handling. So the mainthread opens x other thread. So only this opening must take unter 1 second. After it logic is used, the thread can kill itself and we all are happy, aren't we?
By given the last answers, I will explain my problem:
I try to build an auctioneer site. So I have up to 50 auctions running at the same moment - nothing special. So I need to: every single second look to the auctionlist, see if the time is 00:00:01 and if it is, bid automaticly (it's a feature, that user can create).
So: get 50 objects in a list, iterate through, check if a automatic bid is need, do it.
With 50 objects and the processing time you've given on average you are doing 12 seconds worth of processing every second. Assuming you have 4 cores, you can get this down to an execution time of 4 seconds via threading. Every second. This means that you're going to start off behind and slip further behind as time goes on.
I know you said you tried to think of a way to make it more efficient, but couldn't, but I fear you're going to have to. The problem as stated now is computationally intractable. You're either going to have to process the objects in a rotating window (so each object gets hit once every 4th cycle or so), or you need to make your processing run faster.
First: Profile, if you haven't already. Figure out what section of your code are taking time, etc. I'd go after that database - how long is the I/O of the objects from the database taking? Can you cache that I/O? (If you're manipulating the same 50 objects, don't load them every second.)
Let's address your threads idea: If you want multiple threads, don't create and destroy them every second. Create your X threads, and leave them be -- creating & destroying them are going to be expensive operations. You might find that less threads will work better - such as 1 or 2 per core, as you might be able to reduce time doing context switches.
To expand on Jonathan Leffler's comment on the question, as the OP requested: (This answer is a wiki)
Say you have these three things being auctioned, ending at the times indicated:
10 Apples - ends at 1:05:00 PM
20 Blueberries - ends at 2:00:00 PM
15 Pears - ends at 3:50:00 PM
If the current time is 1:00:00 PM, then sleep for 4 minutes, 58 seconds (since the closest item ends in 5 minutes). We use the 2 seconds then for processing - adjust that threshold as needed. Once we're done with the apples, we'll sleep for (2 PM - now() - 2s), for the blueberries.
Note that when we wake up at 1:04:58 PM to process the apples auction, we do not touch the blueberries or the pears -- we know that they're still way out in the future, so we don't care.