Someone knows how to calculate writing speeds? I need to

Question

C / C++

Mattia

Someone knows how to calculate writing speeds? I need to

calculate the amount of bytes written by consecutives write() calls in a second

0

12.12.2020

23 ответов

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Nader Jafari

Nader Jafari
Idk exactly but i think time.h's time() returns a ...

Well you edited your question to do this each second. You can do this in a new thread and sleep()

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12.12.2020

Mattia Автор вопроса

Nader Jafari
Well you edited your question to do this each seco...

To do so i believe i'd need to add a pthread_lock on the variable of the total bytes written, and considering the sleep not being precise, the lock adding delay for the next writing cycle, i think the calculations would result very wrong. Maybe not all the calculations but probably more than i'd love

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12.12.2020

Cengizhan Pasaoglu

Writing speeds of what? What do you want to measure? Could you please elaborate?

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12.12.2020

Mattia Автор вопроса

Cengizhan Pasaoglu
Writing speeds of what? What do you want to measur...

1. Bytes written in a system call to the write(fd,buf,count) function 2. Bytes per second 3. It is in C, linux, nothing else

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12.12.2020

Kirill 🚜

Mattia
1. Bytes written in a system call to the write(fd,...

Use std::chrono to measure time of writing 1MB of bytes

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12.12.2020

Cengizhan Pasaoglu

Mattia
1. Bytes written in a system call to the write(fd,...

Stıll depends on what kınd of Kernel you have, and what will be jitters at that time. Because, if you don't have real-time patched Kernel on the system. you cannot know that how much you need for writing (you have to collect a few measurement and divide by number of trials) even though some jitters will affect your measurement like SMIs, timers etc.

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12.12.2020

Cengizhan Pasaoglu

Cengizhan Pasaoglu
Stıll depends on what kınd of Kernel you have, and...

You shouldn't guess or ensure how many bytes you can write per second because of these problems.

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12.12.2020

Aakash Saini

Mattia
1. Bytes written in a system call to the write(fd,...

Bytes per second👆

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12.12.2020

Mattia Автор вопроса

Cengizhan Pasaoglu
Stıll depends on what kınd of Kernel you have, and...

Linux raspberrypi 5.4.72-v7l+ #1356 SMP Thu Oct 22 13:57:51 BST 2020 armv7l GNU/Linux

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12.12.2020

Cengizhan Pasaoglu

Mattia
Linux raspberrypi 5.4.72-v7l+ #1356 SMP Thu Oct 22...

I was saying that it depends on many different things. Measurement will be valid only on your machine, and also maybe how many bytes you will write etc, caching, page faults, timers etc. Many parameter can affect on your result.

0

12.12.2020

Mattia Автор вопроса

Cengizhan Pasaoglu
I was saying that it depends on many different thi...

I don't need to use the measurements out of my code, so the results can be considered valid(?) The bytes i write are returned by write(), so it is a precise measure

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12.12.2020

Cengizhan Pasaoglu

Mattia
I don't need to use the measurements out of my cod...

How do you know that when you call write() function, other threads or interrupts on the kernel whether block or not your write() function?

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12.12.2020

Aakash Saini

Mattia
I don't need to use the measurements out of my cod...

👆

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12.12.2020

Mattia Автор вопроса

Aakash Saini
👆

I've tried the code, but i've got to compare it to more precise timing options

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12.12.2020

Aakash Saini

Mattia
I've tried the code, but i've got to compare it to...

More precise like? It’s very precise to function call within start/stop; you just need to fix buffer to bytes.. little code

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12.12.2020

Mattia Автор вопроса

Cengizhan Pasaoglu
How do you know that when you call write() functio...

Hmmm in that case -1 is returned, which is the case in which i have to re-write and don't consider the write output for measurements, making them temporarily non-usable

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12.12.2020

Cengizhan Pasaoglu

Mattia
Hmmm in that case -1 is returned, which is the cas...

Do you have information about Linux Kernel or Operating systems at all?

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12.12.2020

Aakash Saini

Mattia
I've tried the code, but i've got to compare it to...

You can google it too! Here is sample. —> https://mobile.happycodings.com/c//beginners-lab-assignments/code47.html

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12.12.2020

Mattia Автор вопроса

Aakash Saini
More precise like? It’s very precise to function c...

I think that your code makes good measurements only in CPUs with stable and non-adaptable clocks , which isn't always true

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12.12.2020

Mattia Автор вопроса

Cengizhan Pasaoglu
Do you have information about Linux Kernel or Oper...

Kind of, why ask?

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12.12.2020

Cengizhan Pasaoglu

Mattia
Kind of, why ask?

What I was trying to say, you cannot know precisely in user-space how many bytes you can write per second, or you cannot expect to see the same values for each second.

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12.12.2020

Mattia Автор вопроса

Cengizhan Pasaoglu
What I was trying to say, you cannot know precisel...

I absolutely do not expect that always the same values will present. I have not gone into precise details in order to not expand on other topics, but the file descriptor is actually a socket. I am making uploads with that write function

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12.12.2020

Nader Jafari · Accepted Answer

Nader Jafari

Idk exactly but i think time.h's time() returns a long representing milli secs from 1/1/1970 (like its java System class equ) you can simply store it in a var and then substract them from each other after invoking your write() calls

0

12.12.2020

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Someone knows how to calculate writing speeds? I need to

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