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Bandwidth from headphone/microphone jack

I got interested in this after I saw Square use the headphone jack on the iPhone to send credit card data.

What's the average bandwidth of the headphone jack on the iPhone, average notebook, and average mobile device?

Can it be doubled by sending different data streams on the different channels (left/right)?

Gauging a web browser's bandwidth

Is it possible to gauge a web browsers upload and/or download speed by monitoring normal http requests? Ideally a web application would be able to tell the speed of a client without any modifications and without client-side scripting like JavaScript/Java/Flash. So even if a client was accessing the service with a library like Curl it would still work. If this is possible, how? If its not possible, why? How accurate can this method be?

(If it helps assume PHP/Apache, but really this is a platform independent question. Also being able to gauge the upload speed is more important to me.)

How do I simulate a low bandwidth, high latency environment?

I need to simulate a low bandwidth, high latency connection to a server in order to emulate the conditions of a VPN at a remote site. The bandwidth and latency should be tweakable so I can discover the best combination in order to run our software package.

How can I get the current network interface throughput statistics on Linux/UNIX? [closed]

Tools such as MRTG provide network throughput / bandwidth graphs for the current network utilisation on specific interfaces, such as eth0. How can I return that information at the command line on Linux/UNIX?

Preferably this would be without installing anything other than what is available on the system as standard.

How to throttle network traffic for environment simulation?

I'm trying to test an application that uses a database connection. What I would like to do is throttling the bandwith to, say, 1 MBit or such to get a better feeling for the application under realistic conditions.

I already use Wireshark to have a look at the communication with the DB and I expected Wireshark to have a feature like that but as it seems there is no way to do something like that.

Any suggestions?

How to programatically limit bandwidth usage of my c# application?

I've got a backup application here which connects to various webservices and downloads/uploads files from ftp or http servers. What is the easiest way to limit the bandwidth usage of my application?

I need to do that because the application once installed and running will be slowing down internet access for all office people, which eventually will get me into hell. So I'd like to implement a speed-limit which is active during the work-hours and gets disabled at night.

Thanks in advance!

Measuring memory bandwidth from the dot product of two arrays

The dot product of two arrays

for(int i=0; i<n; i++) {
    sum += x[i]*y[i];
}

does not reuse data so it should be a memory bound operation. Therefore, I should be able to measure the memory bandwidth from the dot product.

Using the code at why-vectorizing-the-loop-does-not-have-performance-improvement I get a bandwidth of 9.3 GB/s for my system. However, when I attempt to calculate the bandwidth using the dot product I get over twice the rate for a single thread and over three time the rate using multiple threads (my system has four cores/eight hyper-threads). This makes no sense to me since a memory bound operation should not benefit from multiple threads. Here is the output from the code below:

Xeon E5-1620, GCC 4.9.0, Linux kernel 3.13
dot 1 thread:      1.0 GB, sum 191054.81, time 4.98 s, 21.56 GB/s, 5.39 GFLOPS
dot_avx 1 thread   1.0 GB, sum 191043.33, time 5.16 s, 20.79 GB/s, 5.20 GFLOPS
dot_avx 2 threads: 1.0 GB, sum 191045.34, time 3.44 s, 31.24 GB/s, 7.81 GFLOPS
dot_avx 8 threads: 1.0 GB, sum 191043.34, time 3.26 s, 32.91 GB/s, 8.23 GFLOPS

Can somebody please explain to me why I get over twice the bandwidth for one thread and over three times the bandwidth using more than one thread?

Here is the code I used:

//g++ -O3 -fopenmp -mavx -ffast-math dot.cpp
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <stdint.h>
#include <x86intrin.h>
#include <omp.h>

extern "C" inline float horizontal_add(__m256 a) {
    __m256 t1 = _mm256_hadd_ps(a,a);
    __m256 t2 = _mm256_hadd_ps(t1,t1);
    __m128 t3 = _mm256_extractf128_ps(t2,1);
    __m128 t4 = _mm_add_ss(_mm256_castps256_ps128(t2),t3);
    return _mm_cvtss_f32(t4);
}

extern "C" float dot_avx(float * __restrict x, float * __restrict y, const int n) {
    x = (float*)__builtin_assume_aligned (x, 32);
    y = (float*)__builtin_assume_aligned (y, 32);
    float sum = 0;
    #pragma omp parallel reduction(+:sum)
    {
        __m256 sum1 = _mm256_setzero_ps();
        __m256 sum2 = _mm256_setzero_ps();
        __m256 sum3 = _mm256_setzero_ps();
        __m256 sum4 = _mm256_setzero_ps();
        __m256 x8, y8;
        #pragma omp for
        for(int i=0; i<n; i+=32) {
            x8 = _mm256_loadu_ps(&x[i]);
            y8 = _mm256_loadu_ps(&y[i]);
            sum1 = _mm256_add_ps(_mm256_mul_ps(x8,y8),sum1);
            x8 = _mm256_loadu_ps(&x[i+8]);
            y8 = _mm256_loadu_ps(&y[i+8]);
            sum2 = _mm256_add_ps(_mm256_mul_ps(x8,y8),sum2);
            x8 = _mm256_loadu_ps(&x[i+16]);
            y8 = _mm256_loadu_ps(&y[i+16]);
            sum3 = _mm256_add_ps(_mm256_mul_ps(x8,y8),sum3);
            x8 = _mm256_loadu_ps(&x[i+24]);
            y8 = _mm256_loadu_ps(&y[i+24]);
            sum4 = _mm256_add_ps(_mm256_mul_ps(x8,y8),sum4);
        }
        sum += horizontal_add(_mm256_add_ps(_mm256_add_ps(sum1,sum2),_mm256_add_ps(sum3,sum4)));
    }
    return sum; 
}

extern "C" float dot(float * __restrict x, float * __restrict y, const int n) {
    x = (float*)__builtin_assume_aligned (x, 32);
    y = (float*)__builtin_assume_aligned (y, 32);
    float sum = 0;
    for(int i=0; i<n; i++) {
        sum += x[i]*y[i];
    }
    return sum;
}

int main(){
    uint64_t LEN = 1 << 27;
    float *x = (float*)_mm_malloc(sizeof(float)*LEN,64);
    float *y = (float*)_mm_malloc(sizeof(float)*LEN,64);
    for(uint64_t i=0; i<LEN; i++) { x[i] = 1.0*rand()/RAND_MAX - 0.5; y[i] = 1.0*rand()/RAND_MAX - 0.5;}

    uint64_t size = 2*sizeof(float)*LEN;

    volatile float sum = 0;
    double dtime, rate, flops;  
    int repeat = 100;

    dtime = omp_get_wtime();
    for(int i=0; i<repeat; i++) sum += dot(x,y,LEN);
    dtime = omp_get_wtime() - dtime;
    rate = 1.0*repeat*size/dtime*1E-9;
    flops = 2.0*repeat*LEN/dtime*1E-9;
    printf("%f GB, sum %f, time %f s, %.2f GB/s, %.2f GFLOPS\n", 1.0*size/1024/1024/1024, sum, dtime, rate,flops);

    sum = 0;
    dtime = omp_get_wtime();
    for(int i=0; i<repeat; i++) sum += dot_avx(x,y,LEN);
    dtime = omp_get_wtime() - dtime;
    rate = 1.0*repeat*size/dtime*1E-9;
    flops = 2.0*repeat*LEN/dtime*1E-9;

    printf("%f GB, sum %f, time %f s, %.2f GB/s, %.2f GFLOPS\n", 1.0*size/1024/1024/1024, sum, dtime, rate,flops);
}

I just downloaded, complied, and ran STREAM as suggested by Jonathan Dursi and here are the results:

One thread

Function      Rate (MB/s)   Avg time     Min time     Max time
Copy:       14292.1657       0.0023       0.0022       0.0023
Scale:      14286.0807       0.0023       0.0022       0.0023
Add:        14724.3906       0.0033       0.0033       0.0033
Triad:      15224.3339       0.0032       0.0032       0.0032

Eight threads

Function      Rate (MB/s)   Avg time     Min time     Max time
Copy:       24501.2282       0.0014       0.0013       0.0021
Scale:      23121.0556       0.0014       0.0014       0.0015
Add:        25263.7209       0.0024       0.0019       0.0056
Triad:      25817.7215       0.0020       0.0019       0.0027

Python Requests/urllib — monitoring bandwidth usage

I want to log the total bytes downloaded and uploaded by my Python script.

total_downloaded_bytes = 0
def bandwidth_hook(r, *args, **kwargs):
    global total_downloaded_bytes
    total_downloaded_bytes += len(r.content)
req = requests.session()
req.hooks = {'response': bandwidth_hook}

The above code doesn't take into account HTTP compression (if I'm right) and the size of headers.

Is there a way to count total uploaded and downloaded bytes from a requests.session? If not, what about a script-wide count?

EC2 Instance Types's EXACT Network Performance?

I still can NOT find any exactly mentioned Network Performance details for different EC2 Instance Types, on Amazon. Instead, they are only saying:

• High
• Moderate
• Low

What does is even mean?

• I especially want to know the some exact amount of Traffic-OUT on each Instance Types.

The reason is, i will need to make a LIVE STREAMING and my stream BIT RATE will be 240 kbps. So i need to know which Instance Type can handle how much concurrent viewers.

Thanks & appreciate so much for any nice knowledgeable answer.

Programmatic resource monitoring per process in Linux

I want to know if there is an efficient solution to monitor a process resource consumption (cpu, memory, network bandwidth) in Linux. I want to write a daemon in C++ that does this monitoring for some given PIDs. From what I know, the classic solution is to periodically read the information from /proc, but this doesn't seem the most efficient way (it involves many system calls). For example to monitor the memory usage every second for 50 processes, I have to open, read and close 50 files (that means 150 system calls) every second from /proc. Not to mention the parsing involved when reading these files.

Another problem is the network bandwidth consumption: this cannot be easily computed for each process I want to monitor. The solution adopted by NetHogs involves a pretty high overhead in my opinion: it captures and analyzes every packet using libpcap, then for each packet the local port is determined and searched in /proc to find the corresponding process.

Do you know if there are more efficient alternatives to these methods presented or any libraries that deal with this problems?

Ajax chat polling bandwidth efficiency

I've written a small web application which is basically a JQuery powered chat client within the browser, to get the posts I'm polling the server with an AJAX request and then appending any new replies, I'm worried about making this as efficient as possible while not losing the realtime feel.

http://darklightweb.co.uk/RealTime/

I can't see any way that interrupts are possible so I am polling a page every 5 seconds that returns nothing if no new posts are available to keep data-transfer down if it's idle, if it does have a message the top message in the queue is sent out and I'm checking again as soon as the Ajax request has finished until the message queue is empty.

Any other tips on making this as low-bandwidth as possible or possible alternate implementations?

Socket.IO server performance and bandwidth usage

I'm about to host a small socket server on a local computer and I'd like to know what kind of bandwidth it's going to use. On most days it will have no more than 50 clients connected at once, but once or twice a week it could have as many as 5,000+ clients at once. However, the only messages sent will be an occasional single message to all connected clients at once with no extra data or anything.

Will the server cause a significant drop in performance on the computer it's hosted on or slow down my internet speeds at all?

Server.js:

var app = require('http').createServer(handler)
   , io = require('socket.io').listen(app)
   , fs = require('fs')

 app.listen(8001);

function handler (req, res) {
fs.readFile(__dirname + '/index.html',
  function (err, data) {
    if (err) {
      res.writeHead(500);
      return res.end('Error loading index.html');
    }

    res.writeHead(200);
    res.end(data);
  });
}

io.sockets.on('connection', function (socket) {
  socket.on('SendDefault', function(data) {
    socket.broadcast.emit('GetDefault');
  });
});

Client.js:

setTimeout( function( ){ 
  socket = io.connect('[IP Address]:8001');
  socket.on('GetDefault', function(data) {
    DoStuff( );
  );
} ); }, 10000 );

Does Android lower the download rate when the screen turns off?

I observed that I can download a file faster if I use wget with the screen on application, that acquires a screen dim wake lock than doing the same without this application and having the screen turned off.. I downloaded exactly the same file (from my apache web server) and the time is almost two times faster when I used the screen on application. To download the file I use a ported versions of wget.. And here is my question:

Does Android lower the download rate when the screen turns off?

Or due to the fact that the screen on app acquires a wake lock, forces the CPU to be always on, so more CPU cycles are spent for the download process.. I am a little bit confused..

How to test a site for low bandwidth?

I'm developing a web application for mobile browsers. Right now most of development is done on local machines (with local apache) and I'd like to test how it behaves in low bandwidth and even high latency environments. I don't need to use apache as there is little server side things for the moment. Do you know any good tool?

What bitrate is used for each of the youtube video qualities (360p - 1080p), in regards to flowplayer?

When using flowplayer with the bandwidth check plugin , you need to state the bitrates for the different video quality.

Here what it looks like:

// the bitrates, video width and file names for this clip
      bitrates: [
        { url: "bbb-800.mp4", width: 480, bitrate: 800 },
        { url: "bbb-1200.mp4", width: 720, bitrate: 1200 },
        { url: "bbb-1600.mp4", width: 1080, bitrate: 1600 }
      ],

Which bitrate does a specific quality represent on youtube?

e.g what bitrate does a youtube video playing in 360p quality use?