Need help - Why windows multi-threading data fetch IOPS too fast?!!
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!!
** Purpose: Verify file random read IOPS in comparison with IOMeter
** Author: Nai Yan
** Date: Feb. 9th, 2012
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];
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 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));
So what happens if fread() doesn't return 1? You never issue a
"delete  c"
You also are calling the wrong form of delete (it should be delete). Why not just declare an array of 512?
unsigned char c;
if (fread(&c,512,1,fp) ==1)
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.