Normally, tap always reads packets and simply lets the client drop them if it cannot receive them. For virtio-net, this results in massive packet loss and about an 80% performance loss in TCP throughput.
This patch modifies qemu_send_packet() to only deliver a packet to a VLAN client if it doesn't have a fd_can_read method or the fd_can_read method indicates that it can receive packets. We also return a status of whether any clients were able to receive the packet. If no clients were able to receive a packet, we buffer the packet until a client indicates that it can receive packets again. This patch also modifies the tap code to only read from the tap fd if at least one client on the VLAN is able to receive a packet. Finally, this patch changes the tap code to drain all possible packets from the tap device when the tap fd is readable. Signed-off-by: Anthony Liguori <[EMAIL PROTECTED]> diff --git a/qemu/net.h b/qemu/net.h index 13daa27..dfdf9af 100644 --- a/qemu/net.h +++ b/qemu/net.h @@ -29,7 +29,7 @@ VLANClientState *qemu_new_vlan_client(VLANState *vlan, IOCanRWHandler *fd_can_read, void *opaque); int qemu_can_send_packet(VLANClientState *vc); -void qemu_send_packet(VLANClientState *vc, const uint8_t *buf, int size); +int qemu_send_packet(VLANClientState *vc, const uint8_t *buf, int size); void qemu_handler_true(void *opaque); void do_info_network(void); diff --git a/qemu/vl.c b/qemu/vl.c index c51d704..f4abea3 100644 --- a/qemu/vl.c +++ b/qemu/vl.c @@ -3760,10 +3760,11 @@ int qemu_can_send_packet(VLANClientState *vc1) return 0; } -void qemu_send_packet(VLANClientState *vc1, const uint8_t *buf, int size) +int qemu_send_packet(VLANClientState *vc1, const uint8_t *buf, int size) { VLANState *vlan = vc1->vlan; VLANClientState *vc; + int ret = -EAGAIN; #if 0 printf("vlan %d send:\n", vlan->id); @@ -3771,9 +3772,14 @@ void qemu_send_packet(VLANClientState *vc1, const uint8_t *buf, int size) #endif for(vc = vlan->first_client; vc != NULL; vc = vc->next) { if (vc != vc1) { - vc->fd_read(vc->opaque, buf, size); + if (!vc->fd_can_read || vc->fd_can_read(vc->opaque)) { + vc->fd_read(vc->opaque, buf, size); + ret = 0; + } } } + + return ret; } #if defined(CONFIG_SLIRP) @@ -3976,6 +3982,8 @@ typedef struct TAPState { VLANClientState *vc; int fd; char down_script[1024]; + char buf[4096]; + int size; } TAPState; static void tap_receive(void *opaque, const uint8_t *buf, int size) @@ -3991,24 +3999,70 @@ static void tap_receive(void *opaque, const uint8_t *buf, int size) } } +static int tap_can_send(void *opaque) +{ + TAPState *s = opaque; + VLANClientState *vc; + int can_receive = 0; + + /* Check to see if any of our clients can receive a packet */ + for (vc = s->vc->vlan->first_client; vc; vc = vc->next) { + /* Skip ourselves */ + if (vc == s->vc) + continue; + + if (!vc->fd_can_read) { + /* no fd_can_read handler, they always can receive */ + can_receive = 1; + } else + can_receive = vc->fd_can_read(vc->opaque); + + /* Once someone can receive, we try to send a packet */ + if (can_receive) + break; + } + + return can_receive; +} + static void tap_send(void *opaque) { TAPState *s = opaque; - uint8_t buf[4096]; - int size; + /* First try to send any buffered packet */ + if (s->size > 0) { + int err; + + /* If noone can receive the packet, buffer it */ + err = qemu_send_packet(s->vc, s->buf, s->size); + if (err == -EAGAIN) + return; + } + + /* Read packets until we hit EAGAIN */ + do { #ifdef __sun__ - struct strbuf sbuf; - int f = 0; - sbuf.maxlen = sizeof(buf); - sbuf.buf = buf; - size = getmsg(s->fd, NULL, &sbuf, &f) >=0 ? sbuf.len : -1; + struct strbuf sbuf; + int f = 0; + sbuf.maxlen = sizeof(s->buf); + sbuf.buf = s->buf; + s->size = getmsg(s->fd, NULL, &sbuf, &f) >=0 ? sbuf.len : -1; #else - size = read(s->fd, buf, sizeof(buf)); + s->size = read(s->fd, s->buf, sizeof(s->buf)); #endif - if (size > 0) { - qemu_send_packet(s->vc, buf, size); - } + + if (s->size == -1 && errno == EINTR) + continue; + + if (s->size > 0) { + int err; + + /* If noone can receive the packet, buffer it */ + err = qemu_send_packet(s->vc, s->buf, s->size); + if (err == -EAGAIN) + break; + } + } while (s->size > 0); } /* fd support */ @@ -4022,7 +4076,7 @@ static TAPState *net_tap_fd_init(VLANState *vlan, int fd) return NULL; s->fd = fd; s->vc = qemu_new_vlan_client(vlan, tap_receive, NULL, s); - qemu_set_fd_handler2(s->fd, NULL, tap_send, NULL, s); + qemu_set_fd_handler2(s->fd, tap_can_send, tap_send, NULL, s); snprintf(s->vc->info_str, sizeof(s->vc->info_str), "tap: fd=%d", fd); return s; } ------------------------------------------------------------------------- This SF.net email is sponsored by the 2008 JavaOne(SM) Conference Don't miss this year's exciting event. There's still time to save $100. Use priority code J8TL2D2. http://ad.doubleclick.net/clk;198757673;13503038;p?http://java.sun.com/javaone _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel