paging - why memcpy speed with different sizes from 1 to 256 kb does not show decreasing behavior?

I went on to test memcpy behavior on my system after
seeing this href="https://stackoverflow.com/questions/21038965/why-speed-of-memcpy-drops-dramatically-every-4kb">Why
does the speed of memcpy() drop dramatically every
4KB?

Details of my
system:

arun@arun-OptiPlex-9010:~/mem_copy_test$
            lscpu

Architecture: x86_64
CPU op-mode(s): 32-bit,
            64-bit
Byte Order: Little Endian
CPU(s): 8
On-line CPU(s)
            list: 0-7

Thread(s) per core: 2
Core(s) per socket:
            4
Socket(s): 1
NUMA node(s): 1
Vendor ID:
            GenuineIntel
CPU family: 6
Model: 58
Stepping:
            9
CPU MHz: 1600.000
BogoMIPS:
            6784.45

Virtualization: VT-x
L1d cache: 32K
L1i
            cache: 32K
L2 cache: 256K
L3 cache: 8192K
NUMA node0
            CPU(s): 0-7

arun@arun-OptiPlex-9010:~/mem_copy_test$ cat
            /proc/cpuinfo | grep 'model name'| head -1

model name : Intel(R)
            Core(TM) i7-3770 CPU @
            3.40GHz


arun@arun-OptiPlex-9010:~/mem_copy_test$ uname
            -a

Linux arun-OptiPlex-9010 3.13.0-40-generic #69-Ubuntu
            
SMP Thu Nov 13 17:53:56 UTC 2014 x86_64 x86_64 x86_64
            GNU/Linux

Test
program:

#include
            

#include 
#include
            
#include 

void
            memcpy_speed(unsigned long buf_size, unsigned long iters)
{
 struct
            timeval start, end;
 unsigned char * pbuff_1;
 unsigned char *
            pbuff_2;
 int i;


 pbuff_1 = (void
            *)malloc(buf_size);
 pbuff_2 = (void *)malloc(buf_size);


            gettimeofday(&start, NULL);
 for(i = 0; i < iters; ++i){

            memcpy(pbuff_2, pbuff_1, buf_size);
 } 
 gettimeofday(&end,
            NULL);


 printf("%5.3f\n",
            ((buf_size*iters)/(1.024*1.024))/((end.tv_sec - \

            start.tv_sec)*1000*1000+(end.tv_usec - start.tv_usec)));

            free(pbuff_1);

            free(pbuff_2);
}

main()
{
 unsigned
            long buf_size;
 unsigned int i;

 buf_size = 1;

            for (i = 1; i < 16385 ; i++) {
 printf("bufsize in kb=%d speed=",
            i);
 buf_size = i * 1024;
 memcpy_speed(buf_size, 10000);

            printf("\n");

            }
}

I
am sharing the output from my google drive as stackoverflow is not allowing
me
to post images(says 10 reps needed for
that)

Output for 1 to 256 KB: href="https://drive.google.com/file/d/0B3mnbsS6F4tpY2dhRWJLaEY1RWc/view?usp=sharing"
rel="nofollow
noreferrer">https://drive.google.com/file/d/0B3mnbsS6F4tpY2dhRWJLaEY1RWc/view?usp=sharing

output
for 1 to 16384 KB: href="https://drive.google.com/file/d/0B3mnbsS6F4tpeC1Dd2R1VnJOV2c/view?usp=sharing"
rel="nofollow
noreferrer">https://drive.google.com/file/d/0B3mnbsS6F4tpeC1Dd2R1VnJOV2c/view?usp=sharing

1)
Why the graph has a peak @11-13KB?

2) why
behavior from 20 to 129KB9(range1) and 130 to 256KB(range2) are different?(range1 has
max speed not at multiples of 4 but range2 has max speed at multiples of 4; that too
with large peaks; also range2 has better speed than range1 at multiples of
4)

3) Why the speed reduces
dramatically close to 3000KB?

--Arun