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sort.cpp
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sort.cpp
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/*
* Estimating an effect of various micro optimizations on the
* performance of a standard sorting algorithm.
*
* Sample output:
*
allocated 2147483712 bytes (2.000 GB)
Legend:
ptr - sorting array of pointers
offset - sorting array of offsets (smaller elements)
prefixX - array elements include X bytes prefix of a key
perfect-prefixX - acting as if prefix comparison alone is enough
0:33.670965 ptr
0:33.122159 offset
0:09.144016 prefix8
0:08.886393 perfect-prefix8
0:09.698536 offset-prefix4
0:08.608928 offset-perfect-prefix4
0:09.129550 offset-prefix12
0:09.671609 offset-perfect-prefix12
*
*/
#include <sys/mman.h>
#include <sys/time.h>
#include <err.h>
#include <inttypes.h>
#include <algorithm>
#include <stdio.h>
#include <openssl/md5.h>
struct data_elem
{
unsigned char key[64];
};
void init_data_elem(data_elem &e, size_t ordinal)
{
memset(e.key, 0, sizeof e.key);
MD5((const unsigned char *)&ordinal, sizeof ordinal, e.key);
}
struct benchmark
{
static void *mem;
static size_t memsz;
static data_elem *first;
static size_t n;
static void init(size_t _n, size_t misalign = 0)
{
if (mem) {
if (munmap(mem, memsz)==-1) {
err(EXIT_FAILURE, "munmap");
}
mem = NULL;
}
memsz = (_n + 1) * sizeof (data_elem);
mem = mmap(NULL, memsz, PROT_READ|PROT_WRITE, MAP_ANON|MAP_PRIVATE, -1, 0);
if (!mem) {
err(EXIT_FAILURE, "mmap");
}
first = (data_elem *)((uintptr_t)mem + misalign % sizeof(data_elem));
n = _n;
for (size_t i=0; i<n; i++) {
init_data_elem(*(first+i), i);
}
printf("allocated %zu bytes (%.3f GB)\n", memsz, (float)memsz/1024/1024/1024);
}
template <typename Traits>
static void run(const char *label, const Traits &)
{
typedef typename Traits::sortel sortel;
size_t auxsz = n * sizeof(sortel);
sortel *aux = (sortel *)mmap(NULL, auxsz, PROT_READ|PROT_WRITE, MAP_ANON|MAP_PRIVATE, -1, 0);
if (!aux) {
err(EXIT_FAILURE, "mmap");
}
for (size_t i=0; i<n; i++) {
aux[i].init(*(first+i));
}
timeval start;
if (gettimeofday(&start, NULL)==-1) {
err(EXIT_FAILURE, "gettimeofday");
}
std::sort(aux, aux+n);
timeval end;
if (gettimeofday(&end, NULL)==-1) {
err(EXIT_FAILURE, "gettimeofday");
}
timeval delta;
delta.tv_sec = end.tv_sec - start.tv_sec;
delta.tv_usec = end.tv_usec - start.tv_usec;
if (delta.tv_usec < 0) {
delta.tv_sec -= 1;
delta.tv_usec += 1000000;
}
printf(
"%4d:%02d.%06"PRIdMAX" %s\n",
(int)delta.tv_sec/60, (int)delta.tv_sec%60, (intmax_t)delta.tv_usec,
label);
if (munmap(aux, auxsz)==-1) {
err(EXIT_FAILURE, "munmap");
}
}
};
void *benchmark::mem = NULL;
size_t benchmark::memsz = 0;
data_elem *benchmark::first = 0;
size_t benchmark::n = 0;
/*
* Straightforward - sort element is a pointer to the actual data
*/
struct DefTraits
{
struct sortel
{
data_elem *p;
void init(data_elem &e)
{
p = &e;
}
bool operator < (const sortel &other) const
{
return memcmp(p->key, other.p->key, sizeof p->key)<0;
}
};
};
/*
* Sort element agregates a sort element of some other type and augments
* it with a prefix of the key for faster data comparisons
*/
template<int len, typename T=DefTraits>
struct PrefixTraits
{
struct sortel
{
typename T::sortel nested;
unsigned char prefix[len];
void init(data_elem &e)
{
nested.init(e);
memcpy(prefix, e.key, len);
}
bool operator < (const sortel &other) const
{
int s = memcmp(prefix, other.prefix, len);
return (s ? s<0 : nested<other.nested);
}
};
};
/*
* Since data was allocated in a contiguous chunk offsets of a smaller
* range and consequently of a smaller size than a regular pointer could
* be used
*/
template<typename offset_t = int32_t>
struct OffsetTraits
{
struct sortel
{
offset_t offset;
void init(data_elem &e)
{
offset = (offset_t)(&e - benchmark::first);
}
bool operator < (const sortel &other) const
{
return memcmp((benchmark::first+offset)->key, (benchmark::first+other.offset)->key, sizeof benchmark::first->key)<0;
}
};
};
/*
* This is used to simulate a 'perfect' prefix, i.e. as if it was always
* enough to compare just prefixes to determine data ordering; the
* actual data is never accessed
*/
template<int len>
struct FakeTraits
{
struct sortel
{
unsigned char dummy[len];
void init(data_elem &e)
{
}
bool operator < (const sortel &other) const
{
return false;
}
};
};
int main ()
{
benchmark::init(1<<25, 60);
printf(
"Legend:\n"
"\tptr - sorting array of pointers\n"
"\toffset - sorting array of offsets (smaller elements)\n"
"\tprefixX - array elements include X bytes prefix of a key\n"
"\tperfect-prefixX - acting as if prefix comparison alone is enough\n");
DefTraits d;
benchmark::run("ptr", d);
OffsetTraits<> off;
benchmark::run("offset", d);
PrefixTraits<8> p8;
benchmark::run("prefix8", p8);
PrefixTraits<8, FakeTraits<8> > fake_p8;
benchmark::run("perfect-prefix8", fake_p8);
PrefixTraits<4,OffsetTraits<> > offset_p4;
benchmark::run("offset-prefix4", offset_p4);
PrefixTraits<4,FakeTraits<4> > fake_offset_p4;
benchmark::run("offset-perfect-prefix4", fake_offset_p4);
PrefixTraits<12,OffsetTraits<> > offset_p12;
benchmark::run("offset-prefix12", offset_p12);
PrefixTraits<12,FakeTraits<4> > fake_offset_p12;
benchmark::run("offset-perfect-prefix12", fake_offset_p12);
return 0;
}