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shared: stack allocate GPollFD array in _ctx_integ_source_prepare()

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The prepare() step of the GSource called frequently when the outer
GMainContext is preparing.

In the common case we have

  - few file descriptors in the inner context to track

  - the file descriptors don't change

We also need to consider whether the file descriptors change, because
some book-keeping is necessary when they do. But usually they don't
change.

Hence, let's optimize the prepare step to avoid a heap allocation
in the common case.

Also, because we use nm_utils_g_main_context_create_integrate_source()
with the internal GMainContext of NMClient. That context always has
a small number of file descriptors to track and it doesn't see much
change. In the vast majority of cases, the heap allocation can be
avoided.
This commit is contained in:
Thomas Haller 2021-01-25 14:32:51 +01:00
parent 462668b0c3
commit b26706ca49
No known key found for this signature in database
GPG key ID: 29C2366E4DFC5728
1 changed files with 51 additions and 26 deletions
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77
shared/nm-glib-aux/nm-shared-utils.c
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@ -4799,7 +4799,7 @@ typedef struct {
GMainContext *context;
GHashTable * fds;
GPollFD * fds_arr;
int fds_len;
guint fds_len;
int max_priority;
bool acquired : 1;
} CtxIntegSource;
@ -4842,13 +4842,15 @@ _ctx_integ_source_prepare(GSource *source, int *out_timeout)
int max_priority;
int timeout = -1;
gboolean any_ready;
int fds_allocated;
int fds_len_old;
gs_free GPollFD *fds_arr_old = NULL;
GHashTableIter h_iter;
PollData * poll_data;
gboolean fds_changed;
int i;
GHashTableIter h_iter;
PollData * poll_data;
gboolean fds_changed;
GPollFD new_fds_stack[300u / sizeof(GPollFD)];
gs_free GPollFD *new_fds_heap = NULL;
GPollFD * new_fds;
guint new_fds_len;
guint new_fds_alloc;
guint i;
_CTX_LOG("prepare...");
@ -4856,30 +4858,44 @@ _ctx_integ_source_prepare(GSource *source, int *out_timeout)
any_ready = g_main_context_prepare(ctx_src->context, &max_priority);
fds_arr_old = g_steal_pointer(&ctx_src->fds_arr);
fds_len_old = ctx_src->fds_len;
new_fds_alloc = NM_MAX(G_N_ELEMENTS(new_fds_stack), ctx_src->fds_len);
fds_allocated = NM_MAX(1, fds_len_old); /* there is at least the wakeup's FD */
ctx_src->fds_arr = g_new(GPollFD, fds_allocated);
if (new_fds_alloc > G_N_ELEMENTS(new_fds_stack)) {
new_fds_heap = g_new(GPollFD, new_fds_alloc);
new_fds = new_fds_heap;
} else
new_fds = new_fds_stack;
while ((ctx_src->fds_len = g_main_context_query(ctx_src->context,
max_priority,
&timeout,
ctx_src->fds_arr,
fds_allocated))
> fds_allocated) {
fds_allocated = ctx_src->fds_len;
g_free(ctx_src->fds_arr);
ctx_src->fds_arr = g_new(GPollFD, fds_allocated);
for (;;) {
int l;
nm_assert(new_fds_alloc <= (guint) G_MAXINT);
l = g_main_context_query(ctx_src->context,
max_priority,
&timeout,
new_fds,
(int) new_fds_alloc);
nm_assert(l >= 0);
new_fds_len = (guint) l;
if (G_LIKELY(new_fds_len <= new_fds_alloc))
break;
new_fds_alloc = new_fds_len;
g_free(new_fds_heap);
new_fds_heap = g_new(GPollFD, new_fds_alloc);
new_fds = new_fds_heap;
}
fds_changed = FALSE;
if (fds_len_old != ctx_src->fds_len)
if (new_fds_len != ctx_src->fds_len)
fds_changed = TRUE;
else {
for (i = 0; i < ctx_src->fds_len; i++) {
if (fds_arr_old[i].fd != ctx_src->fds_arr[i].fd
|| fds_arr_old[i].events != ctx_src->fds_arr[i].events) {
for (i = 0; i < new_fds_len; i++) {
if (new_fds[i].fd != ctx_src->fds_arr[i].fd
|| new_fds[i].events != ctx_src->fds_arr[i].events) {
fds_changed = TRUE;
break;
}
@ -4887,6 +4903,13 @@ _ctx_integ_source_prepare(GSource *source, int *out_timeout)
}
if (G_UNLIKELY(fds_changed)) {
g_free(ctx_src->fds_arr);
ctx_src->fds_len = new_fds_len;
if (G_LIKELY(new_fds == new_fds_stack) || new_fds_alloc != new_fds_len)
ctx_src->fds_arr = nm_memdup(new_fds, sizeof(*new_fds) * new_fds_len);
else
ctx_src->fds_arr = g_steal_pointer(&new_fds_heap);
g_hash_table_iter_init(&h_iter, ctx_src->fds);
while (g_hash_table_iter_next(&h_iter, (gpointer *) &poll_data, NULL))
poll_data->stale = TRUE;
@ -5021,10 +5044,12 @@ _ctx_integ_source_check(GSource *source)
ctx_src->fds_arr[poll_data->idx.one].revents = revents;
}
nm_assert(ctx_src->fds_len <= (guint) G_MAXINT);
some_ready = g_main_context_check(ctx_src->context,
ctx_src->max_priority,
ctx_src->fds_arr,
ctx_src->fds_len);
(int) ctx_src->fds_len);
_CTX_LOG("check (some-ready=%d)...", some_ready);