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The networking subsystem may wish to use defer_call(), so move the code to util/ where it can be reused. As a reminder of what defer_call() does: This API defers a function call within a defer_call_begin()/defer_call_end() section, allowing multiple calls to batch up. This is a performance optimization that is used in the block layer to submit several I/O requests at once instead of individually: defer_call_begin(); <-- start of section ... defer_call(my_func, my_obj); <-- deferred my_func(my_obj) call defer_call(my_func, my_obj); <-- another defer_call(my_func, my_obj); <-- another ... defer_call_end(); <-- end of section, my_func(my_obj) is called once Suggested-by: Ilya Maximets <i.maximets@ovn.org> Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> Message-ID: <20230913200045.1024233-3-stefanha@redhat.com> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> Reviewed-by: Kevin Wolf <kwolf@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
157 lines
4.5 KiB
C
157 lines
4.5 KiB
C
/* SPDX-License-Identifier: GPL-2.0-or-later */
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/*
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* Deferred calls
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*
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* Copyright Red Hat.
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*
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* This API defers a function call within a defer_call_begin()/defer_call_end()
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* section, allowing multiple calls to batch up. This is a performance
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* optimization that is used in the block layer to submit several I/O requests
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* at once instead of individually:
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*
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* defer_call_begin(); <-- start of section
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* ...
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* defer_call(my_func, my_obj); <-- deferred my_func(my_obj) call
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* defer_call(my_func, my_obj); <-- another
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* defer_call(my_func, my_obj); <-- another
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* ...
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* defer_call_end(); <-- end of section, my_func(my_obj) is called once
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*/
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#include "qemu/osdep.h"
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#include "qemu/coroutine-tls.h"
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#include "qemu/notify.h"
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#include "qemu/thread.h"
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#include "qemu/defer-call.h"
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/* A function call that has been deferred until defer_call_end() */
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typedef struct {
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void (*fn)(void *);
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void *opaque;
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} DeferredCall;
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/* Per-thread state */
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typedef struct {
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unsigned nesting_level;
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GArray *deferred_call_array;
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} DeferCallThreadState;
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/* Use get_ptr_defer_call_thread_state() to fetch this thread-local value */
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QEMU_DEFINE_STATIC_CO_TLS(DeferCallThreadState, defer_call_thread_state);
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/* Called at thread cleanup time */
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static void defer_call_atexit(Notifier *n, void *value)
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{
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DeferCallThreadState *thread_state = get_ptr_defer_call_thread_state();
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g_array_free(thread_state->deferred_call_array, TRUE);
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}
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/* This won't involve coroutines, so use __thread */
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static __thread Notifier defer_call_atexit_notifier;
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/**
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* defer_call:
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* @fn: a function pointer to be invoked
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* @opaque: a user-defined argument to @fn()
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*
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* Call @fn(@opaque) immediately if not within a
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* defer_call_begin()/defer_call_end() section.
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*
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* Otherwise defer the call until the end of the outermost
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* defer_call_begin()/defer_call_end() section in this thread. If the same
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* @fn/@opaque pair has already been deferred, it will only be called once upon
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* defer_call_end() so that accumulated calls are batched into a single call.
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*
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* The caller must ensure that @opaque is not freed before @fn() is invoked.
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*/
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void defer_call(void (*fn)(void *), void *opaque)
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{
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DeferCallThreadState *thread_state = get_ptr_defer_call_thread_state();
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/* Call immediately if we're not deferring calls */
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if (thread_state->nesting_level == 0) {
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fn(opaque);
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return;
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}
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GArray *array = thread_state->deferred_call_array;
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if (!array) {
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array = g_array_new(FALSE, FALSE, sizeof(DeferredCall));
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thread_state->deferred_call_array = array;
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defer_call_atexit_notifier.notify = defer_call_atexit;
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qemu_thread_atexit_add(&defer_call_atexit_notifier);
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}
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DeferredCall *fns = (DeferredCall *)array->data;
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DeferredCall new_fn = {
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.fn = fn,
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.opaque = opaque,
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};
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/*
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* There won't be many, so do a linear search. If this becomes a bottleneck
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* then a binary search (glib 2.62+) or different data structure could be
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* used.
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*/
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for (guint i = 0; i < array->len; i++) {
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if (memcmp(&fns[i], &new_fn, sizeof(new_fn)) == 0) {
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return; /* already exists */
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}
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}
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g_array_append_val(array, new_fn);
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}
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/**
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* defer_call_begin: Defer defer_call() functions until defer_call_end()
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*
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* defer_call_begin() and defer_call_end() are thread-local operations. The
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* caller must ensure that each defer_call_begin() has a matching
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* defer_call_end() in the same thread.
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*
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* Nesting is supported. defer_call() functions are only called at the
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* outermost defer_call_end().
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*/
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void defer_call_begin(void)
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{
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DeferCallThreadState *thread_state = get_ptr_defer_call_thread_state();
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assert(thread_state->nesting_level < UINT32_MAX);
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thread_state->nesting_level++;
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}
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/**
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* defer_call_end: Run any pending defer_call() functions
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*
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* There must have been a matching defer_call_begin() call in the same thread
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* prior to this defer_call_end() call.
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*/
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void defer_call_end(void)
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{
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DeferCallThreadState *thread_state = get_ptr_defer_call_thread_state();
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assert(thread_state->nesting_level > 0);
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if (--thread_state->nesting_level > 0) {
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return;
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}
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GArray *array = thread_state->deferred_call_array;
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if (!array) {
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return;
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}
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DeferredCall *fns = (DeferredCall *)array->data;
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for (guint i = 0; i < array->len; i++) {
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fns[i].fn(fns[i].opaque);
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}
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/*
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* This resets the array without freeing memory so that appending is cheap
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* in the future.
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*/
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g_array_set_size(array, 0);
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}
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