Re: remove BufferBlockPointers for speed and space

Hello,

With gcc-4 on Ubuntu AMD Athlon 2600 Barton:


jd@jd:~$ ./a.out
duration round 1 of array method: 0.539 ms
duration round 2 of array method: 0.529 ms
duration round 3 of array method: 0.530 ms
duration round 1 of mul method: 0.258 ms
duration round 2 of mul method: 5.563 ms
duration round 3 of mul method: 0.258 ms
duration round 1 of shift method: 0.240 ms
duration round 2 of shift method: 0.248 ms
duration round 3 of shift method: 0.240 ms
jd@jd:~$

Sincerely,

Joshua D. Drake


Qingqing Zhou wrote:

>"Tom Lane" <tgl@sss.pgh.pa.us> writes:
>
>
>>Also, I would like to see the actual test code.  I wonder whether what
>>you measured is the ability of the compiler to optimize references to
>>successive elements of an array inside a loop; that has little or
>>nothing to do with the typical usage of BufferGetBlock().
>>
>>
>>
>
>The source code is attached.
>
>compiled with "gcc testbuf.c". I tried -O2 actually, and it turns out that
>the timing is reduced a lot so not believable.
>---
>
>/*
> * testbuf.c
> */
>#include <stdio.h>
>#include <sys/file.h>
>#include <sys/param.h>
>#include <sys/stat.h>
>#include <sys/time.h>
>#include <unistd.h>
>#include <fcntl.h>
>
>#define BLCKSZ  8192
>#define NBuffers 80000
>
>typedef void* Block;
>
>int main(void)
>{
> int  i, round, method;
> Block k, start;
> struct timeval start_t, stop_t;
> long usecs;
> Block *array = (Block *) calloc(NBuffers, sizeof(Block));
>
> start = (Block)0xff3386;
> for (i = 0; i < NBuffers; i++)
>  array[i] = start + BLCKSZ*i;
>
> for (method = 0; method < 3; method ++)
> {
>  start = (Block)0xff3386;
>  for (round = 0; round < 3; round ++)
>  {
>   gettimeofday(&start_t, NULL);
>   if (method == 0)
>   {
>    for (i = 0; i < NBuffers; i++)
>     k = array[i];
>   }
>   if (method == 1)
>   {
>    for (i = 0; i < NBuffers; i++)
>     k = start + i*BLCKSZ;
>   }
>   if (method == 2)
>   {
>    for (i = 0; i < NBuffers; i++)
>     k = start + (i<<13);
>   }
>   gettimeofday(&stop_t, NULL);
>
>   if (stop_t.tv_usec < start_t.tv_usec)
>   {
>     stop_t.tv_sec--;
>     stop_t.tv_usec += 1000000;
>   }
>
>   usecs = (long) (stop_t.tv_sec - start_t.tv_sec) * 1000000
>     + (long) (stop_t.tv_usec - start_t.tv_usec);
>
>   fprintf (stdout, "duration round %d of %s method: %ld.%03ld ms\n",
>       round + 1,
>       method==0?"array":method==1?"mul":"shift",
>       (long) ((stop_t.tv_sec - start_t.tv_sec) * 1000 +
>         (stop_t.tv_usec - start_t.tv_usec) / 1000),
>       (long) (stop_t.tv_usec - start_t.tv_usec) % 1000);
>  }
> }
>}
>
>
>
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