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Add cache preload facility

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This can do the lstat() storm in parallel, giving potentially much
improved performance for cold-cache cases or things like NFS that have
weak metadata caching.

Just use "read_cache_preload()" instead of "read_cache()" to force an
optimistic preload of the index stat data.  The function takes a
pathspec as its argument, allowing us to preload only the relevant
portion of the index.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Linus Torvalds
2008-11-13 16:36:30 -08:00
committed by Junio C Hamano
parent a0d3ab9c27
commit 671c9b7e31
9 changed files with 122 additions and 10 deletions
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preload-index.c Normal file
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/*
* Copyright (C) 2008 Linus Torvalds
*/
#include "cache.h"
#include <pthread.h>
/*
* Mostly randomly chosen maximum thread counts: we
* cap the parallelism to 20 threads, and we want
* to have at least 500 lstat's per thread for it to
* be worth starting a thread.
*/
#define MAX_PARALLEL (20)
#define THREAD_COST (500)
struct thread_data {
pthread_t pthread;
struct index_state *index;
const char **pathspec;
int offset, nr;
};
static void *preload_thread(void *_data)
{
int nr;
struct thread_data *p = _data;
struct index_state *index = p->index;
struct cache_entry **cep = index->cache + p->offset;
nr = p->nr;
if (nr + p->offset > index->cache_nr)
nr = index->cache_nr - p->offset;
do {
struct cache_entry *ce = *cep++;
struct stat st;
if (ce_stage(ce))
continue;
if (ce_uptodate(ce))
continue;
if (!ce_path_match(ce, p->pathspec))
continue;
if (lstat(ce->name, &st))
continue;
if (ie_match_stat(index, ce, &st, 0))
continue;
ce_mark_uptodate(ce);
} while (--nr > 0);
return NULL;
}
static void preload_index(struct index_state *index, const char **pathspec)
{
int threads, i, work, offset;
struct thread_data data[MAX_PARALLEL];
if (!core_preload_index)
return;
threads = index->cache_nr / THREAD_COST;
if (threads < 2)
return;
if (threads > MAX_PARALLEL)
threads = MAX_PARALLEL;
offset = 0;
work = (index->cache_nr + threads - 1) / threads;
for (i = 0; i < threads; i++) {
struct thread_data *p = data+i;
p->index = index;
p->pathspec = pathspec;
p->offset = offset;
p->nr = work;
offset += work;
if (pthread_create(&p->pthread, NULL, preload_thread, p))
die("unable to create threaded lstat");
}
for (i = 0; i < threads; i++) {
struct thread_data *p = data+i;
if (pthread_join(p->pthread, NULL))
die("unable to join threaded lstat");
}
}
int read_index_preload(struct index_state *index, const char **pathspec)
{
int retval = read_index(index);
preload_index(index, pathspec);
return retval;
}