I found an interesting paper improving index speed by prefetching memory data to L1/L2 cache here (there is discussion about prefetching disk data to memory several days ago "ice-breaker thread"): http://www.cs.cmu.edu/~chensm/papers/index_pf_final.pdf
Also related technique used to speedup memcpy: http://people.redhat.com/arjanv/pIII.c I wonder if we could use it to speed up in-memory scan opertion for heap or index. Tom's patch has made scan can handle a page (vs. row) every time, which is a basis for this optimization. I write a program try to simulate it, but I am not good at micro optimization, and I just get a very weak but kind-of-stable improvement. I wonder if any people here are interested to take a look. Regards, Qingqing ---------------------------------- Test results -------------- Cache line size: 64 CPU: P4 2.4G $#./prefetch 10 16 Sum: -951304192: with prefetch on - duration: 42.163 ms Sum: -951304192: with prefetch off - duration: 42.838 ms Sum: -951304192: with prefetch on - duration: 44.044 ms Sum: -951304192: with prefetch off - duration: 42.792 ms Sum: -951304192: with prefetch on - duration: 42.324 ms Sum: -951304192: with prefetch off - duration: 42.803 ms Sum: -951304192: with prefetch on - duration: 42.189 ms Sum: -951304192: with prefetch off - duration: 42.801 ms Sum: -951304192: with prefetch on - duration: 42.155 ms Sum: -951304192: with prefetch off - duration: 42.827 ms Sum: -951304192: with prefetch on - duration: 42.179 ms Sum: -951304192: with prefetch off - duration: 42.798 ms Sum: -951304192: with prefetch on - duration: 42.180 ms Sum: -951304192: with prefetch off - duration: 42.804 ms Sum: -951304192: with prefetch on - duration: 42.193 ms Sum: -951304192: with prefetch off - duration: 42.827 ms Sum: -951304192: with prefetch on - duration: 42.164 ms Sum: -951304192: with prefetch off - duration: 42.810 ms Sum: -951304192: with prefetch on - duration: 42.182 ms Sum: -951304192: with prefetch off - duration: 42.826 ms Test program ---------------- /* * prefetch.c * PostgreSQL warm-cache sequential scan simulator with prefetch */ #include <stdio.h> #include <stdlib.h> #include <memory.h> #include <errno.h> #include <sys/time.h> typedef char bool; #define true ((bool) 1) #define false ((bool) 0) #define BLCKSZ 8192 #define CACHESZ 64 #define NBLCKS 5000 int sum; int main(int argc, char *argv[]) { int i, rounds; char *blocks; int cpu_cost; if (argc != 3) { fprintf(stderr, "usage: prefetch <rounds> <cpu_cost [1, 16]>\n"); exit(-1); } rounds = atoi(argv[1]); cpu_cost = atoi(argv[2]); if (cpu_cost > 16) exit(-1); for (i = 0; i < 2*rounds; i++) { int j, k; struct timeval start_t, stop_t; bool enable = i%2?false:true; char *blck; blocks = (char *)malloc(BLCKSZ*NBLCKS); memset(blocks, 'a', BLCKSZ*NBLCKS); sum = 0; gettimeofday(&start_t, NULL); for (j = 0; j < NBLCKS; j++) { blck = blocks + j*BLCKSZ; for (k=0; k < BLCKSZ; k+=CACHESZ) { int *s = (int *)(blck + k); int u = cpu_cost; if (enable) { /* prefetch ahead */ __asm__ __volatile__ ( "1: prefetchnta 128(%0)\n" : : "r" (s) : "memory" ); } /* pretend to process current tuple */ while (u--) sum += (*(s+u))*(*(s+u)); } } gettimeofday(&stop_t, NULL); free(blocks); /* measure the time */ if (stop_t.tv_usec < start_t.tv_usec) { stop_t.tv_sec--; stop_t.tv_usec += 1000000; } fprintf (stdout, "Sum: %d: with prefetch %s - duration: %ld.%03ld ms\n", sum, enable?"on":"off", (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); } exit(0); } ---------------------------(end of broadcast)--------------------------- TIP 1: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
