Need help - Why windows multi-threading data fetch IOPS too fast?!!
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  1. #1
    Join Date
    Feb 2012
    Posts
    1

    Need help - Why windows multi-threading data fetch IOPS too fast?!!

    Greetings,
    Can anybody help me a little out of my difficulty?

    I have a SSD and I am trying to use it to simulate my program I/O performance, however, IOPS calculated from my program is much much faster than IOMeter.

    My SSD is PLEXTOR PX-128M3S, by IOMeter, its max 512B random read IOPS is around 94k (queue depth is 32).
    However my program (32 windows threads) can reach around 500k 512B IOPS, around 5 times of IOMeter!!! I did data validation but didn't find any error in data fetching. It's because my data fetching in order?

    I paste my code belwo (it mainly fetch 512B from file and release it; I did use 4bytes (an int) to validate program logic and didn't find problem), can anybody help me figure out where I am wrong?

    Thanks so much in advance!!

    Nai Yan.

    #include <stdio.h>
    #include <Windows.h>

    /*
    ** Purpose: Verify file random read IOPS in comparison with IOMeter
    ** Author: Nai Yan
    ** Date: Feb. 9th, 2012
    **/

    //Global variables
    long completeIOs = 0;
    long completeBytes = 0;
    int threadCount = 32;
    unsigned long long length = 1073741824; //4G test file

    int interval = 1024;

    int resultArrayLen = 320000;

    int *result = new int[resultArrayLen];

    //Method declarison
    double GetSecs(void); //Calculate out duration
    int InitPool(long long,char*,int); //Initialize test data for testing, if successful, return 1; otherwise, return a non 1 value.
    int * FileRead(char * path);
    unsigned int DataVerification(int*, int sampleItem); //Verify data fetched from pool

    int main()
    {
    int sampleItem = 0x1;
    char * fPath = "G:\\workspace\\4G.bin";
    unsigned int invalidIO = 0;

    if (InitPool(length,fPath,sampleItem)!= 1)
    printf("File write err... \n");

    //start do random I/Os from initialized file
    double start = GetSecs();

    int * fetchResult = FileRead(fPath);

    double end = GetSecs();

    printf("File read IOPS is %.4f per second.. \n",completeIOs/(end - start));

    //start data validation, for 4 bytes fetch only

    // invalidIO = DataVerification(fetchResult,sampleItem);

    // if (invalidIO !=0)
    // {
    // printf("Total invalid data fetch IOs are %d", invalidIO);
    // }

    return 0;
    }



    int InitPool(long long length, char* path, int sample)
    {
    printf("Start initializing test data ... \n");

    FILE * fp = fopen(path,"wb");

    if (fp == NULL)
    {
    printf("file open err... \n");
    exit (-1);
    }

    else //initialize file for testing
    {
    fseek(fp,0L,SEEK_SET);

    for (int i=0; i<length; i++)
    {
    fwrite(&sample,sizeof(int),1,fp);
    }

    fclose(fp);

    fp = NULL;

    printf("Data initialization is complete...\n");

    return 1;

    }
    }

    double GetSecs(void)

    {
    LARGE_INTEGER frequency;
    LARGE_INTEGER start;

    if(! QueryPerformanceFrequency(&frequency))
    printf("QueryPerformanceFrequency Failed\n");

    if(! QueryPerformanceCounter(&start))
    printf("QueryPerformanceCounter Failed\n");

    return ((double)start.QuadPart/(double)frequency.QuadPart);

    }

    class input
    {
    public:
    char *path;
    int starting;

    input (int st, char * filePath):starting(st),path(filePath){}

    };

    //Workers
    DWORD WINAPI FileReadThreadEntry(LPVOID lpThreadParameter)
    {
    input * in = (input*) lpThreadParameter;

    char* path = in->path;

    FILE * fp = fopen(path,"rb");

    int sPos = in->starting;

    // int * result = in->r;

    if(fp != NULL)
    {
    fpos_t pos;
    for (int i=0; i<resultArrayLen/threadCount;i++)
    {

    pos = i * interval;
    fsetpos(fp,&pos);
    //For 512 bytes fetch each time
    unsigned char *c =new unsigned char [512];
    if (fread(c,512,1,fp) ==1)
    {
    InterlockedIncrement(&completeIOs);
    delete c;
    }

    //For 4 bytes fetch each time
    /*if (fread(&result[sPos + i],sizeof(int),1,fp) ==1)
    {
    InterlockedIncrement(&completeIOs);
    }*/

    else
    {
    printf("file read err...\n");
    exit(-1);
    }
    }

    fclose(fp);
    fp = NULL;
    }

    else
    {
    printf("File open err... \n");
    exit(-1);
    }
    }

    int * FileRead(char * p)
    {
    printf("Starting reading file ... \n");


    HANDLE mWorkThread[256]; //max 256 threads
    completeIOs = 0;

    int slice = int (resultArrayLen/threadCount);

    for(int i = 0; i < threadCount; i++)
    {
    mWorkThread[i] = CreateThread(
    NULL,
    0,
    FileReadThreadEntry,
    (LPVOID)(new input(i*slice,p)),
    0,
    NULL);
    }

    WaitForMultipleObjects(threadCount, mWorkThread, TRUE, INFINITE);

    printf("File read complete... \n");

    return result;

    }

    unsigned int DataVerification(int* result, int sampleItem)
    {
    unsigned int invalid = 0;
    for (int i=0; i< resultArrayLen/interval;i++)
    {
    if (result[i]!=sampleItem)
    {
    invalid ++;
    continue;
    }
    }

    return invalid;
    }

  2. #2
    Join Date
    Apr 1999
    Posts
    27,446

    Re: Need help - Why windows multi-threading data fetch IOPS too fast?!!

    Quote Originally Posted by zhaonaiy View Post
    Greetings,
    Can anybody help me a little out of my difficulty?
    First use code tags when posting code. Your code is unreadable without them.

    Second, your program has memory leaks. If you're going to test a program, it needs to be correct first.
    Code:
    unsigned char *c =new unsigned char [512];
    if (fread(c,512,1,fp) ==1)
    {
    	InterlockedIncrement(&completeIOs);
    	delete c;
    }
    So what happens if fread() doesn't return 1? You never issue a
    Code:
    "delete [] c"
    You also are calling the wrong form of delete (it should be delete[]). Why not just declare an array of 512?
    Code:
    unsigned char c[512];
    if (fread(&c,512,1,fp) ==1)
    {
    	InterlockedIncrement(&completeIOs);
    }
    Lastly, you're throwing in timing the allocator (new[] / new / delete/delete[]) in your code. That makes all of your timing tests biased, as the allocator could be the biggest bottleneck in all of your code.

    Regards,

    Paul McKenzie

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