Slow memcpy speed

An update:

When defining arrays like this

int value[2048]; //source array

int dest[2048] ; //destination array

and running memcpy(dest,value,2048*4), memcpy speed is high: 446 Mbytes/s

And the compile flag -Ofast give faster speed than -O1, as expected.

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My design is based upon the fpga_fft example from Rocketboard where DMA transfers data from FPGA into HPS’s DRAM memory.

The memory space for these data (*value) is defined using mmap:

volatile unsigned int *value;

volatile unsigned int dest[2048*4];

# define result_base (FFT_SUB_DATA_BASE + (int)mappedbase +(FFT_SUB_DATA_SPAN/2))

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In main:

// we need to get a pointer to the LW_BRIDGE from the softwares point of view.

// need to open a file.

/* Open /dev/mem */

if ((mem = open("/dev/mem", O_RDWR | O_SYNC)) == -1)

fprintf(stderr, "Cannot open /dev/mem\n"), exit(1);

// now map it into lw bridge space:

mappedbase = mmap(0, 0x1f0000, prot_read | prot_write, map_shared, mem, alt_lwfpgaslvs_ofst);

if (mappedBase == (void *)-1) {

printf("Memory map failed. error %i\n", (int)mappedBase);

perror("mmap");

}

Run DMA and wait for completion

...

...

// And when the DMA is finnished the data is available:

value = (unsigned int *)((int)result_base);

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Now, when running memcpy(dest,value,2048*4) the speed is slow: only 42 Mbytes/s, and the compiler does not respond as expected to the -O compiler flags, i.e. -Ofast is slower that -O1.

It seems that using mmap really slows down the access to memory. Is it possible to speed this up?

Any help would be greatly appreciated!

Thanks,