select: Optimize osmo_fd_get_by_fd

Optimize osmo_fd_get_by_fd() from O(n) to O(k) by means of allocating
dynamically growing array.

Make use from the fact that the kernel always tries to use the smallest
 possible unused value when allocating a new fd.

Change-Id: I8b71547df8bed84192cb160479fa3debf9b7eade
This commit is contained in:
Pau Espin 2023-03-09 17:37:15 +01:00 committed by pespin
parent b7bf36f81c
commit c46a15d876
1 changed files with 44 additions and 8 deletions

View File

@ -54,6 +54,39 @@ static __thread int maxfd = 0;
static __thread struct llist_head osmo_fds; /* TLS cannot use LLIST_HEAD() */
static __thread int unregistered_count;
/* Array of struct osmo_fd * (size "max_fd") ordered by "ofd->fd" */
static __thread struct {
struct osmo_fd **table;
unsigned int size;
} osmo_fd_lookup;
static void osmo_fd_lookup_table_extend(unsigned int new_max_fd)
{
unsigned int min_new_size;
unsigned int pw2;
unsigned int new_size;
/* First calculate the minimally required new size of the array in bytes: */
min_new_size = (new_max_fd + 1) * sizeof(struct osmo_fd *);
/* Now find the lower power of two of min_new_size (in bytes): */
pw2 = 32 - __builtin_clz(min_new_size);
/* get next (upper side) power of 2: */
pw2++;
OSMO_ASSERT(pw2 <= 31); /* Avoid shifting more than 31 bits */
new_size = 1 << (pw2 + 1);
/* Let's make it at least 1024B, to avoid reallocating quickly at startup */
if (new_size < 1024)
new_size = 1024;
if (new_size > osmo_fd_lookup.size) {
uint8_t *ptr = talloc_realloc_size(OTC_GLOBAL, osmo_fd_lookup.table, new_size);
OSMO_ASSERT(ptr);
memset(ptr + osmo_fd_lookup.size, 0, new_size - osmo_fd_lookup.size);
osmo_fd_lookup.table = (struct osmo_fd **)ptr;
osmo_fd_lookup.size = new_size;
}
}
#ifndef FORCE_IO_SELECT
struct poll_state {
/* array of pollfd */
@ -142,8 +175,10 @@ int osmo_fd_register(struct osmo_fd *fd)
return flags;
/* Register FD */
if (fd->fd > maxfd)
if (fd->fd > maxfd) {
maxfd = fd->fd;
osmo_fd_lookup_table_extend(maxfd);
}
#ifdef OSMO_FD_CHECK
if (osmo_fd_is_registered(fd)) {
@ -166,6 +201,7 @@ int osmo_fd_register(struct osmo_fd *fd)
#endif /* FORCE_IO_SELECT */
llist_add_tail(&fd->list, &osmo_fds);
osmo_fd_lookup.table[fd->fd] = fd;
return 0;
}
@ -180,6 +216,9 @@ void osmo_fd_unregister(struct osmo_fd *fd)
* osmo_fd_is_registered() */
unregistered_count++;
llist_del(&fd->list);
OSMO_ASSERT(fd->fd >= 0);
OSMO_ASSERT(fd->fd <= maxfd);
osmo_fd_lookup.table[fd->fd] = NULL;
#ifndef FORCE_IO_SELECT
g_poll.num_registered--;
#endif /* FORCE_IO_SELECT */
@ -464,19 +503,16 @@ int osmo_select_main_ctx(int polling)
* \returns \ref osmo_fd for \ref fd; NULL in case it doesn't exist */
struct osmo_fd *osmo_fd_get_by_fd(int fd)
{
struct osmo_fd *ofd;
llist_for_each_entry(ofd, &osmo_fds, list) {
if (ofd->fd == fd)
return ofd;
}
return NULL;
if (fd > maxfd)
return NULL;
return osmo_fd_lookup.table[fd];
}
/*! initialize the osmocom select abstraction for the current thread */
void osmo_select_init(void)
{
INIT_LLIST_HEAD(&osmo_fds);
osmo_fd_lookup_table_extend(0);
}
/* ensure main thread always has pre-initialized osmo_fds */