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authorPaolo Bonzini <pbonzini@redhat.com>2011-09-19 15:25:40 +0200
committerPaolo Bonzini <pbonzini@redhat.com>2011-12-22 11:53:59 +0100
commit41996e3803119541d43bfa59060024a22b803342 (patch)
tree59a003a257c875ee6479d5ed0a9ee4e35f383ccf /nbd.c
parent262db38871b9a2613761cc5f05c4cf697e246a68 (diff)
downloadqemu-arm-41996e3803119541d43bfa59060024a22b803342.tar.gz
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: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'nbd.c')
-rw-r--r--nbd.c25
1 files changed, 22 insertions, 3 deletions
diff --git a/nbd.c b/nbd.c
index 6d7d1f8d59..567e94e27a 100644
--- a/nbd.c
+++ b/nbd.c
@@ -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;
}