Commit 41996e38 authored by Paolo Bonzini's avatar Paolo Bonzini
Browse files

qemu-nbd: throttle requests 



Limiting the number of in-flight requests is implemented very simply
with a can_read callback.  It does not require a semaphore, unlike the
client side in block/nbd.c, because we can throttle directly the creation
of coroutines.  The client side can have a coroutine created at any time
when an I/O request is made.

Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 262db388

nbd.c

+22 −3
Original line number Diff line number Diff line
@@ -587,6 +587,8 @@ static int nbd_send_reply(int csock, struct nbd_reply *reply) 
    return 0;

}



#define MAX_NBD_REQUESTS 16



typedef struct NBDRequest NBDRequest;



struct NBDRequest {
@@ -614,6 +616,8 @@ struct NBDClient { 


    CoMutex send_lock;

    Coroutine *send_coroutine;



    int nb_requests;

};



static void nbd_client_get(NBDClient *client)
@@ -644,6 +648,9 @@ static NBDRequest *nbd_request_get(NBDClient *client) 
    NBDRequest *req;

    NBDExport *exp = client->exp;



    assert(client->nb_requests <= MAX_NBD_REQUESTS - 1);

    client->nb_requests++;



    if (QSIMPLEQ_EMPTY(&exp->requests)) {

        req = g_malloc0(sizeof(NBDRequest));

        req->data = qemu_blockalign(exp->bs, NBD_BUFFER_SIZE);
@@ -660,6 +667,9 @@ static void nbd_request_put(NBDRequest *req) 
{

    NBDClient *client = req->client;

    QSIMPLEQ_INSERT_HEAD(&client->exp->requests, req, entry);

    if (client->nb_requests-- == MAX_NBD_REQUESTS) {

        qemu_notify_event();

    }

    nbd_client_put(client);

}
@@ -688,6 +698,7 @@ void nbd_export_close(NBDExport *exp) 
    g_free(exp);

}



static int nbd_can_read(void *opaque);

static void nbd_read(void *opaque);

static void nbd_restart_write(void *opaque);
@@ -699,7 +710,8 @@ static int nbd_co_send_reply(NBDRequest *req, struct nbd_reply *reply, 
    int rc, ret;



    qemu_co_mutex_lock(&client->send_lock);

    qemu_set_fd_handler2(csock, NULL, nbd_read, nbd_restart_write, client);

    qemu_set_fd_handler2(csock, nbd_can_read, nbd_read,

                         nbd_restart_write, client);

    client->send_coroutine = qemu_coroutine_self();



    if (!len) {
@@ -724,7 +736,7 @@ static int nbd_co_send_reply(NBDRequest *req, struct nbd_reply *reply, 
    }



    client->send_coroutine = NULL;

    qemu_set_fd_handler2(csock, NULL, nbd_read, NULL, client);

    qemu_set_fd_handler2(csock, nbd_can_read, nbd_read, NULL, client);

    qemu_co_mutex_unlock(&client->send_lock);

    return rc;

}
@@ -900,6 +912,13 @@ out: 
    nbd_client_close(client);

}



static int nbd_can_read(void *opaque)

{

    NBDClient *client = opaque;



    return client->recv_coroutine || client->nb_requests < MAX_NBD_REQUESTS;

}



static void nbd_read(void *opaque)

{

    NBDClient *client = opaque;
@@ -931,6 +950,6 @@ NBDClient *nbd_client_new(NBDExport *exp, int csock, 
    client->sock = csock;

    client->close = close;

    qemu_co_mutex_init(&client->send_lock);

    qemu_set_fd_handler2(csock, NULL, nbd_read, NULL, client);

    qemu_set_fd_handler2(csock, nbd_can_read, nbd_read, NULL, client);

    return client;

}