[ovs-dev] [PATCH v2] dpif-netlink: distribute polling to discreet handlers
Flavio Leitner
fbl at sysclose.org
Thu Aug 6 20:35:06 UTC 2020
Hi Aaron,
Thanks for the patch. I ran some basic tests here
and they passed. I could see only one handler thread
becoming active with a single upcall.
See my comment below.
On Tue, Jul 21, 2020 at 07:27:41PM -0400, Aaron Conole wrote:
> Currently, the channel handlers are polled globally. On some
> systems, this causes a thundering herd issue where multiple
> handler threads become active, only to do no work and immediately
> sleep.
>
> The approach here is to push the netlink socket channels to discreet
> handler threads to process, rather than polling on every thread.
> This will eliminate the need to wake multiple threads.
>
> To check:
>
> ip netns add left
> ip netns add right
> ip link add center-left type veth peer name left0
> ip link add center-right type veth peer name right0
> ip link set left0 netns left
> ip link set right0 netns right
> ip link set center-left up
> ip link set center-right up
> ip -n left ip link set left0 up
> ip -n left ip addr add 172.31.110.10/24 dev left0
> ip -n right ip link set right0 up
> ip -n right ip addr add 172.31.110.11/24 dev right0
>
> ovs-vsctl add-br br0
> ovs-vsctl add-port br0 center-right
> ovs-vsctl add-port br0 center-left
>
> # in one terminal
> perf record -e sched:sched_wakeup,irq:softirq_entry -ag
>
> # in a separate terminal
> ip netns exec left arping -I left0 -c 1 172.31.110.11
>
> # in the perf terminal after exiting
> perf script
>
> Look for the number of 'handler' threads which were made active.
>
> Suggested-by: Ben Pfaff <blp at ovn.org>
> Reported-by: David Ahern <dsahern at gmail.com>
> Reported-at: https://mail.openvswitch.org/pipermail/ovs-dev/2019-December/365857.html
> Cc: Matteo Croce <technoboy85 at gmail.com>
> Cc: Flavio Leitner <fbl at sysclose.org>
> Fixes: 69c51582f ("dpif-netlink: don't allocate per thread netlink sockets")
> Signed-off-by: Aaron Conole <aconole at redhat.com>
> ---
> v2: Oops - forgot to commit my whitespace cleanups.
>
> lib/dpif-netlink.c | 289 ++++++++++++++++++++++++++++-----------------
> 1 file changed, 179 insertions(+), 110 deletions(-)
>
> diff --git a/lib/dpif-netlink.c b/lib/dpif-netlink.c
> index 7da4fb54d9..71d2805427 100644
> --- a/lib/dpif-netlink.c
> +++ b/lib/dpif-netlink.c
> @@ -183,6 +183,10 @@ struct dpif_handler {
> int n_events; /* Num events returned by epoll_wait(). */
> int event_offset; /* Offset into 'epoll_events'. */
>
> + struct dpif_channel *channels; /* Array of channels for each port. */
> + uint32_t *port_idx_map; /* Port idx to channel idx. */
> + size_t n_channels;
> +
> #ifdef _WIN32
> /* Pool of sockets. */
> struct dpif_windows_vport_sock *vport_sock_pool;
> @@ -202,8 +206,6 @@ struct dpif_netlink {
> struct dpif_handler *handlers;
> uint32_t n_handlers; /* Num of upcall handlers. */
> struct dpif_channel *channels; /* Array of channels for each port. */
Shouldn't the above channels be removed?
> - int uc_array_size; /* Size of 'handler->channels' and */
> - /* 'handler->epoll_events'. */
>
> /* Change notification. */
> struct nl_sock *port_notifier; /* vport multicast group subscriber. */
> @@ -287,6 +289,55 @@ close_nl_sock(struct nl_sock *sock)
> #endif
> }
>
> +static uint32_t
> +dpif_handler_port_idx_max(const struct dpif_handler *handler,
> + struct dpif_channel **out_chn)
Looks like there is no caller passing out_chn, so why
that is needed?
> +{
> + uint32_t max = 0;
> + size_t i;
> +
> + for (i = 0; i < handler->n_channels; ++i) {
OVS does have some code using '++i', but the majority of
it uses 'i++', can you please swap them?
> + if (handler->channels[i].sock &&
> + handler->port_idx_map[i] > max) {
> + max = handler->port_idx_map[i];
> + if (out_chn) {
> + *out_chn = &handler->channels[i];
> + }
> + }
> + }
> +
> + return max;
> +}
> +
> +static size_t
> +dpif_handler_active_channels(const struct dpif_handler *handler)
> +{
> + size_t i, ret = 0;
Perhaps 'count' or 'num' would be a better name.
> +
> + for (i = 0; i < handler->n_channels; ++i) {
> + if (handler->channels[i].sock) {
> + ret++;
> + }
> + }
> +
> + return ret;
> +}
> +
> +static struct dpif_channel *
> +dpif_handler_has_port_idx(const struct dpif_handler *handler, uint32_t idx)
> +{
> + size_t i;
> +
> + for (i = 0; i < handler->n_channels; ++i) {
> + if (handler->channels[i].sock &&
> + handler->port_idx_map[i] == idx) {
> + return &handler->channels[i];
> + }
> + }
> +
> + return NULL;
> +}
> +
> static struct dpif_netlink *
> dpif_netlink_cast(const struct dpif *dpif)
> {
> @@ -452,90 +503,86 @@ static bool
> vport_get_pid(struct dpif_netlink *dpif, uint32_t port_idx,
> uint32_t *upcall_pid)
> {
> - /* Since the nl_sock can only be assigned in either all
> - * or none "dpif" channels, the following check
> - * would suffice. */
> - if (!dpif->channels[port_idx].sock) {
> - return false;
> - }
> + size_t i;
> +
> ovs_assert(!WINDOWS || dpif->n_handlers <= 1);
>
> - *upcall_pid = nl_sock_pid(dpif->channels[port_idx].sock);
> + /* The 'port_idx' should only be valid for a single handler. */
> + for (i = 0; i < dpif->n_handlers; ++i) {
> + struct dpif_channel *channel =
> + dpif_handler_has_port_idx(&dpif->handlers[i], port_idx);
> +
> + if (channel) {
> + *upcall_pid = nl_sock_pid(channel->sock);
> + return true;
> + }
> + }
>
> - return true;
> + return false;
> }
>
> static int
> vport_add_channel(struct dpif_netlink *dpif, odp_port_t port_no,
> struct nl_sock *sock)
> {
> - struct epoll_event event;
> uint32_t port_idx = odp_to_u32(port_no);
> + struct dpif_handler *handler;
> + struct dpif_channel *channel;
> + struct epoll_event event;
> + int error = 0;
> size_t i;
> - int error;
>
> if (dpif->handlers == NULL) {
> close_nl_sock(sock);
> - return 0;
> + return error;
> }
>
> - /* We assume that the datapath densely chooses port numbers, which can
> - * therefore be used as an index into 'channels' and 'epoll_events' of
> - * 'dpif'. */
> - if (port_idx >= dpif->uc_array_size) {
> - uint32_t new_size = port_idx + 1;
> + handler = &dpif->handlers[0];
>
> - if (new_size > MAX_PORTS) {
> - VLOG_WARN_RL(&error_rl, "%s: datapath port %"PRIu32" too big",
> - dpif_name(&dpif->dpif), port_no);
> - return EFBIG;
> - }
Could you please explain why checking MAX_PORTS is not
important anymore? If it isn't, then this should remove
MAX_PORT declaration as that was the only use.
> -
> - dpif->channels = xrealloc(dpif->channels,
> - new_size * sizeof *dpif->channels);
> + for (i = 0; i < dpif->n_handlers; ++i) {
> + if (dpif_handler_active_channels(&dpif->handlers[i]) <
> + dpif_handler_active_channels(handler))
> + handler = &dpif->handlers[i];
> + }
>
> - for (i = dpif->uc_array_size; i < new_size; i++) {
> - dpif->channels[i].sock = NULL;
> + channel = NULL;
> + for (i = 0; i < handler->n_channels; ++i) {
> + if (!handler->channels[i].sock) {
> + channel = &handler->channels[i];
> + handler->port_idx_map[i] = port_idx;
> }
> + }
>
> - for (i = 0; i < dpif->n_handlers; i++) {
> - struct dpif_handler *handler = &dpif->handlers[i];
> -
> - handler->epoll_events = xrealloc(handler->epoll_events,
> - new_size * sizeof *handler->epoll_events);
> -
> - }
> - dpif->uc_array_size = new_size;
> + if (channel == NULL) {
> + size_t new_size = handler->n_channels + 1;
> + handler->channels = xrealloc(handler->channels,
> + new_size * sizeof *handler->channels);
> + handler->epoll_events = xrealloc(handler->epoll_events,
> + new_size *
> + sizeof *handler->epoll_events);
> + handler->port_idx_map = xrealloc(handler->port_idx_map,
> + new_size *
> + sizeof *handler->port_idx_map);
> + channel = &handler->channels[handler->n_channels];
> + handler->port_idx_map[handler->n_channels] = port_idx;
> + i = handler->n_channels;
> + handler->n_channels += 1;
perhaps handler->n_channels = new_size to remove the magic number?
> }
>
> + channel->sock = sock;
> + channel->last_poll = LLONG_MIN;
> +
> memset(&event, 0, sizeof event);
> event.events = EPOLLIN | EPOLLEXCLUSIVE;
> - event.data.u32 = port_idx;
> -
> - for (i = 0; i < dpif->n_handlers; i++) {
> - struct dpif_handler *handler = &dpif->handlers[i];
> + event.data.u32 = i;
>
> #ifndef _WIN32
> - if (epoll_ctl(handler->epoll_fd, EPOLL_CTL_ADD, nl_sock_fd(sock),
> - &event) < 0) {
> - error = errno;
> - goto error;
> - }
> -#endif
> - }
> - dpif->channels[port_idx].sock = sock;
> - dpif->channels[port_idx].last_poll = LLONG_MIN;
> -
> - return 0;
> -
> -error:
> -#ifndef _WIN32
> - while (i--) {
> - epoll_ctl(dpif->handlers[i].epoll_fd, EPOLL_CTL_DEL,
> - nl_sock_fd(sock), NULL);
> + if (epoll_ctl(handler->epoll_fd, EPOLL_CTL_ADD, nl_sock_fd(sock),
> + &event) < 0) {
> + error = errno;
> + channel->sock = NULL;
> }
> #endif
> - dpif->channels[port_idx].sock = NULL;
>
> return error;
> }
> @@ -544,69 +591,81 @@ static void
> vport_del_channels(struct dpif_netlink *dpif, odp_port_t port_no)
> {
> uint32_t port_idx = odp_to_u32(port_no);
> + struct dpif_handler *handler = NULL;
> + struct dpif_channel *channel = NULL;
> size_t i;
>
> - if (!dpif->handlers || port_idx >= dpif->uc_array_size
> - || !dpif->channels[port_idx].sock) {
> + if (!dpif->handlers) {
> return;
> }
>
> - for (i = 0; i < dpif->n_handlers; i++) {
> - struct dpif_handler *handler = &dpif->handlers[i];
> + for (i = 0; i < dpif->n_handlers && channel == NULL; i++) {
> + handler = &dpif->handlers[i];
> + channel = dpif_handler_has_port_idx(handler, port_idx);
> +
> + if (channel == NULL) {
> + continue;
> + }
> +
> #ifndef _WIN32
> epoll_ctl(handler->epoll_fd, EPOLL_CTL_DEL,
> - nl_sock_fd(dpif->channels[port_idx].sock), NULL);
> + nl_sock_fd(channel->sock), NULL);
> #endif
> handler->event_offset = handler->n_events = 0;
> }
> +
> + if (channel) {
> #ifndef _WIN32
> - nl_sock_destroy(dpif->channels[port_idx].sock);
> + nl_sock_destroy(channel->sock);
> #endif
> - dpif->channels[port_idx].sock = NULL;
> + channel->sock = NULL;
Ok, so it doesn't resize the memory when ports are removed.
I was wondering if it wouldn't scale better if we use hmaps and
id_pools instead:
--- a/lib/dpif-netlink.c
+++ b/lib/dpif-netlink.c
@@ -183,9 +183,7 @@ struct dpif_handler {
int n_events; /* Num events returned by epoll_wait(). */
int event_offset; /* Offset into 'epoll_events'. */
- struct dpif_channel *channels; /* Array of channels for each port. */
- uint32_t *port_idx_map; /* Port idx to channel idx. */
- size_t n_channels;
+ struct hmap channels; /* Channels for each port. */
#ifdef _WIN32
/* Pool of sockets. */
@@ -205,7 +203,7 @@ struct dpif_netlink {
struct fat_rwlock upcall_lock;
struct dpif_handler *handlers;
uint32_t n_handlers; /* Num of upcall handlers. */
- struct dpif_channel *channels; /* Array of channels for each port. */
+ struct id_pool *port_ids; /* Pool of port ids. */
/* Change notification. */
struct nl_sock *port_notifier; /* vport multicast group subscriber. */
For instance, we can find the least loaded with just hmap_count() instead
of iterating on all handlers and ports. Also when we add/remove a port, we
could use HMAP_FOR_EACH_WITH_HASH() using port_id as hash to find the
channel.
What do you think?
> + }
> }
>
> static void
> destroy_all_channels(struct dpif_netlink *dpif)
> OVS_REQ_WRLOCK(dpif->upcall_lock)
> {
> - unsigned int i;
> + size_t i, j;
>
> if (!dpif->handlers) {
> return;
> }
>
> - for (i = 0; i < dpif->uc_array_size; i++ ) {
> - struct dpif_netlink_vport vport_request;
> - uint32_t upcall_pids = 0;
> + for (i = 0; i < dpif->n_handlers; ++i) {
nitpick: Same comment as before to change to 'i++'
> + struct dpif_handler *handler = &dpif->handlers[i];
>
> - if (!dpif->channels[i].sock) {
> - continue;
> - }
> + for (j = 0; j < handler->n_channels; ++j) {
and here
> + struct dpif_netlink_vport vport_request;
> + uint32_t upcall_pids = 0;
>
> - /* Turn off upcalls. */
> - dpif_netlink_vport_init(&vport_request);
> - vport_request.cmd = OVS_VPORT_CMD_SET;
> - vport_request.dp_ifindex = dpif->dp_ifindex;
> - vport_request.port_no = u32_to_odp(i);
> - vport_request.n_upcall_pids = 1;
> - vport_request.upcall_pids = &upcall_pids;
> - dpif_netlink_vport_transact(&vport_request, NULL, NULL);
> + if (!handler->channels[j].sock) {
> + continue;
> + }
>
> - vport_del_channels(dpif, u32_to_odp(i));
> - }
> + /* Turn off upcalls. */
> + dpif_netlink_vport_init(&vport_request);
> + vport_request.cmd = OVS_VPORT_CMD_SET;
> + vport_request.dp_ifindex = dpif->dp_ifindex;
> + vport_request.port_no = u32_to_odp(handler->port_idx_map[j]);
> + vport_request.n_upcall_pids = 1;
> + vport_request.upcall_pids = &upcall_pids;
> + dpif_netlink_vport_transact(&vport_request, NULL, NULL);
>
> - for (i = 0; i < dpif->n_handlers; i++) {
> - struct dpif_handler *handler = &dpif->handlers[i];
> + vport_del_channels(dpif, u32_to_odp(handler->port_idx_map[j]));
> + }
>
> dpif_netlink_handler_uninit(handler);
> + handler->n_channels = 0;
> +
> free(handler->epoll_events);
> + free(handler->port_idx_map);
> + free(handler->channels);
> }
> - free(dpif->channels);
> +
> free(dpif->handlers);
> dpif->handlers = NULL;
> - dpif->channels = NULL;
> dpif->n_handlers = 0;
> - dpif->uc_array_size = 0;
> }
>
> static void
> @@ -1084,23 +1143,31 @@ dpif_netlink_port_get_pid__(const struct dpif_netlink *dpif,
> odp_port_t port_no)
> OVS_REQ_RDLOCK(dpif->upcall_lock)
> {
> + struct dpif_channel *min_channel = NULL, *found_channel = NULL;
> uint32_t port_idx = odp_to_u32(port_no);
> uint32_t pid = 0;
>
> - if (dpif->handlers && dpif->uc_array_size > 0) {
> - /* The ODPP_NONE "reserved" port number uses the "ovs-system"'s
> - * channel, since it is not heavily loaded. */
> - uint32_t idx = port_idx >= dpif->uc_array_size ? 0 : port_idx;
> -
> - /* Needs to check in case the socket pointer is changed in between
> - * the holding of upcall_lock. A known case happens when the main
> - * thread deletes the vport while the handler thread is handling
> - * the upcall from that port. */
> - if (dpif->channels[idx].sock) {
> - pid = nl_sock_pid(dpif->channels[idx].sock);
> + if (dpif->handlers) {
> + size_t i;
> + for (i = 0; i < dpif->n_handlers; ++i) {
> + if (dpif_handler_has_port_idx(&dpif->handlers[i], port_idx)) {
> + found_channel = dpif_handler_has_port_idx(&dpif->handlers[i],
> + port_idx);
> + }
> +
> + if (dpif_handler_has_port_idx(&dpif->handlers[i], 0)) {
> + min_channel = dpif_handler_has_port_idx(&dpif->handlers[i],
> + 0);
> + }
> }
The comment about the ODPP_NONE reserved port seems still relevant.
Also, if it finds a channel, couldn't it just break the loop?
> }
>
> + if (found_channel) {
> + pid = nl_sock_pid(found_channel->sock);
> + } else if (min_channel) {
> + pid = nl_sock_pid(min_channel->sock);
> + }
> +
> return pid;
> }
>
> @@ -2376,7 +2443,7 @@ dpif_netlink_refresh_channels(struct dpif_netlink *dpif, uint32_t n_handlers)
> {
> unsigned long int *keep_channels;
> struct dpif_netlink_vport vport;
> - size_t keep_channels_nbits;
> + size_t keep_channels_nbits = 0;
> struct nl_dump dump;
> uint64_t reply_stub[NL_DUMP_BUFSIZE / 8];
> struct ofpbuf buf;
> @@ -2414,9 +2481,11 @@ dpif_netlink_refresh_channels(struct dpif_netlink *dpif, uint32_t n_handlers)
> struct dpif_handler *handler = &dpif->handlers[i];
>
> handler->event_offset = handler->n_events = 0;
> + if (keep_channels_nbits < dpif_handler_port_idx_max(handler, NULL)) {
> + keep_channels_nbits = dpif_handler_port_idx_max(handler, NULL);
> + }
> }
>
> - keep_channels_nbits = dpif->uc_array_size;
> keep_channels = bitmap_allocate(keep_channels_nbits);
>
> ofpbuf_use_stub(&buf, reply_stub, sizeof reply_stub);
> @@ -2426,8 +2495,7 @@ dpif_netlink_refresh_channels(struct dpif_netlink *dpif, uint32_t n_handlers)
> uint32_t upcall_pid;
> int error;
>
> - if (port_no >= dpif->uc_array_size
> - || !vport_get_pid(dpif, port_no, &upcall_pid)) {
> + if (!vport_get_pid(dpif, port_no, &upcall_pid)) {
> struct nl_sock *sock;
> error = create_nl_sock(dpif, &sock);
>
> @@ -2721,14 +2789,14 @@ dpif_netlink_recv__(struct dpif_netlink *dpif, uint32_t handler_id,
> }
>
> handler = &dpif->handlers[handler_id];
> - if (handler->event_offset >= handler->n_events) {
> + if (handler->event_offset >= handler->n_events && handler->n_channels) {
> int retval;
>
> handler->event_offset = handler->n_events = 0;
>
> do {
> retval = epoll_wait(handler->epoll_fd, handler->epoll_events,
> - dpif->uc_array_size, 0);
> + handler->n_channels, 0);
> } while (retval < 0 && errno == EINTR);
>
> if (retval < 0) {
> @@ -2741,7 +2809,7 @@ dpif_netlink_recv__(struct dpif_netlink *dpif, uint32_t handler_id,
>
> while (handler->event_offset < handler->n_events) {
> int idx = handler->epoll_events[handler->event_offset].data.u32;
> - struct dpif_channel *ch = &dpif->channels[idx];
> + struct dpif_channel *ch = &handler->channels[idx];
>
> handler->event_offset++;
>
> @@ -2845,12 +2913,13 @@ dpif_netlink_recv_purge__(struct dpif_netlink *dpif)
> if (dpif->handlers) {
> size_t i;
>
> - if (!dpif->channels[0].sock) {
> - return;
> - }
> - for (i = 0; i < dpif->uc_array_size; i++ ) {
> + for (i = 0; i < dpif->n_handlers; i++) {
> + struct dpif_handler *handler = &dpif->handlers[i];
> + size_t j;
>
> - nl_sock_drain(dpif->channels[i].sock);
> + for (j = 0; j < handler->n_channels; ++j) {
> + nl_sock_drain(handler->channels[j].sock);
> + }
> }
> }
> }
> --
> 2.25.4
>
> _______________________________________________
> dev mailing list
> dev at openvswitch.org
> https://mail.openvswitch.org/mailman/listinfo/ovs-dev
--
fbl
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