From 41996e3803119541d43bfa59060024a22b803342 Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Mon, 19 Sep 2011 15:25:40 +0200 Subject: 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 --- nbd.c | 25 ++++++++++++++++++++++--- 1 file changed, 22 insertions(+), 3 deletions(-) (limited to 'nbd.c') diff --git a/nbd.c b/nbd.c index 6d7d1f8d5..567e94e27 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; } -- cgit v1.2.3