Commit 4749079c authored by Stefan Hajnoczi's avatar Stefan Hajnoczi
Browse files

aio-posix: make AioHandler deletion O(1) 



It is not necessary to scan all AioHandlers for deletion.  Keep a list
of deleted handlers instead of scanning the full list of all handlers.

The AioHandler->deleted field can be dropped.  Let's check if the
handler has been inserted into the deleted list instead.  Add a new
QLIST_IS_INSERTED() API for this check.

Signed-off-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: default avatarSergio Lopez <slp@redhat.com>
Message-id: 20200214171712.541358-5-stefanha@redhat.com
Signed-off-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
parent 195ed8cb

include/block/aio.h

+5 −1
Original line number Diff line number Diff line
@@ -42,6 +42,7 @@ void qemu_aio_unref(void *p); 
void qemu_aio_ref(void *p);



typedef struct AioHandler AioHandler;

typedef QLIST_HEAD(, AioHandler) AioHandlerList;

typedef void QEMUBHFunc(void *opaque);

typedef bool AioPollFn(void *opaque);

typedef void IOHandler(void *opaque);
@@ -71,7 +72,10 @@ struct AioContext { 
    QemuRecMutex lock;



    /* The list of registered AIO handlers.  Protected by ctx->list_lock. */

    QLIST_HEAD(, AioHandler) aio_handlers;

    AioHandlerList aio_handlers;



    /* The list of AIO handlers to be deleted.  Protected by ctx->list_lock. */

    AioHandlerList deleted_aio_handlers;



    /* Used to avoid unnecessary event_notifier_set calls in aio_notify;

     * accessed with atomic primitives.  If this field is 0, everything

include/qemu/queue.h

+3 −0
Original line number Diff line number Diff line
@@ -158,6 +158,9 @@ struct { \ 
        }                                                               \

} while (/*CONSTCOND*/0)



/* Is elm in a list? */

#define QLIST_IS_INSERTED(elm, field) ((elm)->field.le_prev != NULL)



#define QLIST_FOREACH(var, head, field)                                 \

        for ((var) = ((head)->lh_first);                                \

                (var);                                                  \

util/aio-posix.c

+35 −18
Original line number Diff line number Diff line
@@ -32,10 +32,10 @@ struct AioHandler 
    AioPollFn *io_poll;

    IOHandler *io_poll_begin;

    IOHandler *io_poll_end;

    int deleted;

    void *opaque;

    bool is_external;

    QLIST_ENTRY(AioHandler) node;

    QLIST_ENTRY(AioHandler) node_deleted;

};



#ifdef CONFIG_EPOLL_CREATE1
@@ -68,7 +68,7 @@ static bool aio_epoll_try_enable(AioContext *ctx) 


    QLIST_FOREACH_RCU(node, &ctx->aio_handlers, node) {

        int r;

        if (node->deleted || !node->pfd.events) {

        if (QLIST_IS_INSERTED(node, node_deleted) || !node->pfd.events) {

            continue;

        }

        event.events = epoll_events_from_pfd(node->pfd.events);
@@ -196,10 +196,12 @@ static AioHandler *find_aio_handler(AioContext *ctx, int fd) 
    AioHandler *node;



    QLIST_FOREACH(node, &ctx->aio_handlers, node) {

        if (node->pfd.fd == fd)

            if (!node->deleted)

        if (node->pfd.fd == fd) {

            if (!QLIST_IS_INSERTED(node, node_deleted)) {

                return node;

            }

        }

    }



    return NULL;

}
@@ -217,7 +219,7 @@ static bool aio_remove_fd_handler(AioContext *ctx, AioHandler *node) 


    /* If a read is in progress, just mark the node as deleted */

    if (qemu_lockcnt_count(&ctx->list_lock)) {

        node->deleted = 1;

        QLIST_INSERT_HEAD_RCU(&ctx->deleted_aio_handlers, node, node_deleted);

        node->pfd.revents = 0;

        return false;

    }
@@ -359,7 +361,7 @@ static void poll_set_started(AioContext *ctx, bool started) 
    QLIST_FOREACH_RCU(node, &ctx->aio_handlers, node) {

        IOHandler *fn;



        if (node->deleted) {

        if (QLIST_IS_INSERTED(node, node_deleted)) {

            continue;

        }
@@ -416,6 +418,26 @@ bool aio_pending(AioContext *ctx) 
    return result;

}



static void aio_free_deleted_handlers(AioContext *ctx)

{

    AioHandler *node;



    if (QLIST_EMPTY_RCU(&ctx->deleted_aio_handlers)) {

        return;

    }

    if (!qemu_lockcnt_dec_if_lock(&ctx->list_lock)) {

        return; /* we are nested, let the parent do the freeing */

    }



    while ((node = QLIST_FIRST_RCU(&ctx->deleted_aio_handlers))) {

        QLIST_REMOVE(node, node);

        QLIST_REMOVE(node, node_deleted);

        g_free(node);

    }



    qemu_lockcnt_inc_and_unlock(&ctx->list_lock);

}



static bool aio_dispatch_handlers(AioContext *ctx)

{

    AioHandler *node, *tmp;
@@ -427,7 +449,7 @@ static bool aio_dispatch_handlers(AioContext *ctx) 
        revents = node->pfd.revents & node->pfd.events;

        node->pfd.revents = 0;



        if (!node->deleted &&

        if (!QLIST_IS_INSERTED(node, node_deleted) &&

            (revents & (G_IO_IN | G_IO_HUP | G_IO_ERR)) &&

            aio_node_check(ctx, node->is_external) &&

            node->io_read) {
@@ -438,21 +460,13 @@ static bool aio_dispatch_handlers(AioContext *ctx) 
                progress = true;

            }

        }

        if (!node->deleted &&

        if (!QLIST_IS_INSERTED(node, node_deleted) &&

            (revents & (G_IO_OUT | G_IO_ERR)) &&

            aio_node_check(ctx, node->is_external) &&

            node->io_write) {

            node->io_write(node->opaque);

            progress = true;

        }



        if (node->deleted) {

            if (qemu_lockcnt_dec_if_lock(&ctx->list_lock)) {

                QLIST_REMOVE(node, node);

                g_free(node);

                qemu_lockcnt_inc_and_unlock(&ctx->list_lock);

            }

        }

    }



    return progress;
@@ -463,6 +477,7 @@ void aio_dispatch(AioContext *ctx) 
    qemu_lockcnt_inc(&ctx->list_lock);

    aio_bh_poll(ctx);

    aio_dispatch_handlers(ctx);

    aio_free_deleted_handlers(ctx);

    qemu_lockcnt_dec(&ctx->list_lock);



    timerlistgroup_run_timers(&ctx->tlg);
@@ -530,7 +545,7 @@ static bool run_poll_handlers_once(AioContext *ctx, int64_t *timeout) 
    RCU_READ_LOCK_GUARD();



    QLIST_FOREACH_RCU(node, &ctx->aio_handlers, node) {

        if (!node->deleted && node->io_poll &&

        if (!QLIST_IS_INSERTED(node, node_deleted) && node->io_poll &&

            aio_node_check(ctx, node->is_external) &&

            node->io_poll(node->opaque)) {

            /*
@@ -664,7 +679,7 @@ bool aio_poll(AioContext *ctx, bool blocking) 


        if (!aio_epoll_enabled(ctx)) {

            QLIST_FOREACH_RCU(node, &ctx->aio_handlers, node) {

                if (!node->deleted && node->pfd.events

                if (!QLIST_IS_INSERTED(node, node_deleted) && node->pfd.events

                    && aio_node_check(ctx, node->is_external)) {

                    add_pollfd(node);

                }
@@ -741,6 +756,8 @@ bool aio_poll(AioContext *ctx, bool blocking) 
        progress |= aio_dispatch_handlers(ctx);

    }



    aio_free_deleted_handlers(ctx);



    qemu_lockcnt_dec(&ctx->list_lock);



    progress |= timerlistgroup_run_timers(&ctx->tlg);