[ovs-dev] [PATCH v7] ovsdb: provide raft and command interfaces with priority
Ilya Maximets
i.maximets at ovn.org
Tue Aug 10 22:06:04 UTC 2021
On 7/27/21 10:21 AM, anton.ivanov at cambridgegreys.com wrote:
> From: Anton Ivanov <anton.ivanov at cambridgegreys.com>
>
> Set a soft time limit of "raft election timer"/2 on ovsdb
> processing.
>
> This improves behaviour in large heavily loaded clusters.
> While it cannot fully eliminate spurious raft elections
> under heavy load, it significantly decreases their number.
>
> Processing is (to the extent possible) restarted where it
> stopped on the previous iteration to ensure that sessions
> towards the tail of the session list are not starved.
>
> Signed-off-by: Anton Ivanov <anton.ivanov at cambridgegreys.com>
> ---
> ovsdb/jsonrpc-server.c | 90 ++++++++++++++++++++++++++++++++++++++++--
> ovsdb/jsonrpc-server.h | 2 +-
> ovsdb/ovsdb-server.c | 16 +++++++-
> ovsdb/raft.c | 6 +++
> ovsdb/raft.h | 3 ++
> ovsdb/storage.c | 12 ++++++
> ovsdb/storage.h | 2 +
> 7 files changed, 125 insertions(+), 6 deletions(-)
>
> diff --git a/ovsdb/jsonrpc-server.c b/ovsdb/jsonrpc-server.c
> index 351c39d8a..ea82d4161 100644
> --- a/ovsdb/jsonrpc-server.c
> +++ b/ovsdb/jsonrpc-server.c
> @@ -60,7 +60,8 @@ static struct ovsdb_jsonrpc_session *ovsdb_jsonrpc_session_create(
> struct ovsdb_jsonrpc_remote *, struct jsonrpc_session *, bool);
> static void ovsdb_jsonrpc_session_preremove_db(struct ovsdb_jsonrpc_remote *,
> struct ovsdb *);
> -static void ovsdb_jsonrpc_session_run_all(struct ovsdb_jsonrpc_remote *);
> +static void ovsdb_jsonrpc_session_run_all(struct ovsdb_jsonrpc_remote *,
> + uint64_t limit);
> static void ovsdb_jsonrpc_session_wait_all(struct ovsdb_jsonrpc_remote *);
> static void ovsdb_jsonrpc_session_get_memory_usage_all(
> const struct ovsdb_jsonrpc_remote *, struct simap *usage);
> @@ -128,6 +129,11 @@ struct ovsdb_jsonrpc_server {
> bool read_only; /* This server is does not accept any
> transactions that can modify the database. */
> struct shash remotes; /* Contains "struct ovsdb_jsonrpc_remote *"s. */
> + struct ovsdb_jsonrpc_remote *skip_to; /* Pointer to remote where processing
> + should restart after a time
> + constraint interruption. */
> + bool must_wake_up; /* The processing loop must be re-run. It was
> + interrupted due to exceeding a time constraint. */
> };
>
> /* A configured remote. This is either a passive stream listener plus a list
> @@ -137,6 +143,9 @@ struct ovsdb_jsonrpc_remote {
> struct ovsdb_jsonrpc_server *server;
> struct pstream *listener; /* Listener, if passive. */
> struct ovs_list sessions; /* List of "struct ovsdb_jsonrpc_session"s. */
> + struct ovsdb_jsonrpc_session *skip_to; /* Session at which processing
> + should restart after an
> + interruption. */
> uint8_t dscp;
> bool read_only;
> char *role;
> @@ -279,6 +288,7 @@ ovsdb_jsonrpc_server_add_remote(struct ovsdb_jsonrpc_server *svr,
> remote->dscp = options->dscp;
> remote->read_only = options->read_only;
> remote->role = nullable_xstrdup(options->role);
> + remote->skip_to = NULL;
> shash_add(&svr->remotes, name, remote);
>
> if (!listener) {
> @@ -293,6 +303,9 @@ ovsdb_jsonrpc_server_del_remote(struct shash_node *node)
> {
> struct ovsdb_jsonrpc_remote *remote = node->data;
>
> + /* The safest option is to rerun all remotes. */
> + remote->server->skip_to = NULL;
> +
> ovsdb_jsonrpc_session_close_all(remote);
> pstream_close(remote->listener);
> shash_delete(&remote->server->remotes, node);
> @@ -378,12 +391,24 @@ ovsdb_jsonrpc_server_set_read_only(struct ovsdb_jsonrpc_server *svr,
> }
>
> void
> -ovsdb_jsonrpc_server_run(struct ovsdb_jsonrpc_server *svr)
> +ovsdb_jsonrpc_server_run(struct ovsdb_jsonrpc_server *svr, uint64_t limit)
> {
> struct shash_node *node;
> + uint64_t elapsed = 0;
> + uint64_t start_time = time_msec();
> +
> + svr->must_wake_up = false;
>
> SHASH_FOR_EACH (node, &svr->remotes) {
> struct ovsdb_jsonrpc_remote *remote = node->data;
> + if (svr->skip_to) {
> + if (remote != svr->skip_to) {
> + continue;
> + } else {
> + svr->skip_to = NULL;
> + svr->must_wake_up = true;
> + }
> + }
>
> if (remote->listener) {
> struct stream *stream;
> @@ -403,7 +428,17 @@ ovsdb_jsonrpc_server_run(struct ovsdb_jsonrpc_server *svr)
> }
> }
>
> - ovsdb_jsonrpc_session_run_all(remote);
> + /* We assume accept and session creation time to be
> + * negligible for the purposes of computing timeouts.
> + */
> + ovsdb_jsonrpc_session_run_all(remote, limit - elapsed);
> +
> + elapsed = time_msec() - start_time;
> + if (elapsed > limit) {
> + svr->must_wake_up = true;
> + svr->skip_to = remote;
> + break;
> + }
> }
> }
>
> @@ -412,6 +447,16 @@ ovsdb_jsonrpc_server_wait(struct ovsdb_jsonrpc_server *svr)
> {
> struct shash_node *node;
>
> + if (svr->must_wake_up) {
> + /* We have stopped processing due to a time constraint.
> + * In this case there is no point to walk all sessions
> + * and rebuild the poll structure for the poll loop.
The last sentence seems redundant. We need to wake up because there
is work that we didn't finish. This module should not reference
internals of the poll_loop.
> + */
> + poll_immediate_wake();
> + svr->must_wake_up = false;
> + return;
> + }
> +
> SHASH_FOR_EACH (node, &svr->remotes) {
> struct ovsdb_jsonrpc_remote *remote = node->data;
>
> @@ -583,15 +628,52 @@ ovsdb_jsonrpc_session_set_options(struct ovsdb_jsonrpc_session *session,
> }
>
> static void
> -ovsdb_jsonrpc_session_run_all(struct ovsdb_jsonrpc_remote *remote)
> +ovsdb_jsonrpc_session_run_all(struct ovsdb_jsonrpc_remote *remote,
> + uint64_t limit)
> {
> struct ovsdb_jsonrpc_session *s, *next;
> + uint64_t start_time = time_msec();
>
> LIST_FOR_EACH_SAFE (s, next, node, &remote->sessions) {
> + if (remote->skip_to && s != remote->skip_to) {
> + /* Processing was interrupted, we skip to the point
> + * where we had to interrupt it.
> + * We cannot use the _CONTINUE macro as it is not safe
> + * if the list has been changed in the meantime.
> + */
> + continue;
> + }
> +
> + /* Set ->next as skip point if we need to restart processing.
> + * This way, even if current is removed, we always have a
> + * valid pointer to continue processing.
Hmm, but what if the 'next' will be removed? In this case we will not
have a valid pointer.
> + */
> + remote->skip_to =
> + CONTAINER_OF(ovs_list_front(&s->node),
> + struct ovsdb_jsonrpc_session, node);
> +
> + if (remote->skip_to == s) {
> + /* The list is a singleton. This is a special case, where
> + * deleting the node will invalidate the pointer.
> + */
> + remote->skip_to = NULL;
Assuming we have several remotes and one of them has only one session,
but this session is extremely heavy in a way that their processing
always take longer than limit (this can be a session that spams
with monitor requests or constantly changes conditions that triggers
the walk across the database, or something else). So, at the exit
of ovsdb_jsonrpc_session_run_all(), remote->skip_to will be NULL.
And ovsdb_jsonrpc_server_run() will have svr->skip_to set to the
same remote. This way ovsdb-server will serve only this one hungry
session and will never serve any other clients on other remotes.
> + }
> +
> int error = ovsdb_jsonrpc_session_run(s);
> if (error) {
> ovsdb_jsonrpc_session_close(s);
> }
> +
> + if (time_msec() - start_time > limit) {
> + /* We bail leaving skip_to set. Next processing iteration
> + * will skip everything up to skip_to which was set to
> + * ->next earlier on.
> + */
> + break;
> + } else {
> + /* We are within time constraints, clear skip_to. */
> + remote->skip_to = NULL;
> + }
> }
> }
>
> diff --git a/ovsdb/jsonrpc-server.h b/ovsdb/jsonrpc-server.h
> index e0653aa39..218152e9d 100644
> --- a/ovsdb/jsonrpc-server.h
> +++ b/ovsdb/jsonrpc-server.h
> @@ -67,7 +67,7 @@ void ovsdb_jsonrpc_server_free_remote_status(
> void ovsdb_jsonrpc_server_reconnect(struct ovsdb_jsonrpc_server *, bool force,
> char *comment);
>
> -void ovsdb_jsonrpc_server_run(struct ovsdb_jsonrpc_server *);
> +void ovsdb_jsonrpc_server_run(struct ovsdb_jsonrpc_server *, uint64_t limit);
> void ovsdb_jsonrpc_server_wait(struct ovsdb_jsonrpc_server *);
>
> void ovsdb_jsonrpc_server_set_read_only(struct ovsdb_jsonrpc_server *,
> diff --git a/ovsdb/ovsdb-server.c b/ovsdb/ovsdb-server.c
> index 0b3d2bb71..ed43da968 100644
> --- a/ovsdb/ovsdb-server.c
> +++ b/ovsdb/ovsdb-server.c
> @@ -216,7 +216,21 @@ main_loop(struct server_config *config,
> reconfigure_remotes(jsonrpc, all_dbs, remotes),
> &remotes_error);
> report_error_if_changed(reconfigure_ssl(all_dbs), &ssl_error);
> - ovsdb_jsonrpc_server_run(jsonrpc);
> +
> + /* Figure out current processing time limit. */
> + uint64_t limit = UINT64_MAX;
> + SHASH_FOR_EACH (node, all_dbs) {
> + struct db *db = node->data;
> + uint64_t db_limit;
> +
> + db_limit = ovsdb_storage_max_processing_time(db->db->storage);
> + limit = MIN(db_limit, limit);
> + }
> + if (ovs_replay_is_active()) {
> + limit = UINT64_MAX;
> + }
Suggesting to move this code to a separate function, e.g.
static uint64_t *get_max_processing_time(const struct shash *all_dbs);
And only leave a call here:
uint64_t limit = get_max_processing_time(all_dbs);
> +
> + ovsdb_jsonrpc_server_run(jsonrpc, limit);
>
> if (*is_backup) {
> replication_run();
> diff --git a/ovsdb/raft.c b/ovsdb/raft.c
> index 2fb515651..183463aba 100644
> --- a/ovsdb/raft.c
> +++ b/ovsdb/raft.c
> @@ -407,6 +407,12 @@ raft_make_address_passive(const char *address_)
> }
> }
>
> +uint64_t
> +raft_get_election_timer(const struct raft *raft)
> +{
> + return raft->election_timer;
> +}
> +
> static struct raft *
> raft_alloc(void)
> {
> diff --git a/ovsdb/raft.h b/ovsdb/raft.h
> index 3545c41c2..575e7f609 100644
> --- a/ovsdb/raft.h
> +++ b/ovsdb/raft.h
> @@ -188,4 +188,7 @@ void raft_take_leadership(struct raft *);
> void raft_transfer_leadership(struct raft *, const char *reason);
>
> const struct uuid *raft_current_eid(const struct raft *);
> +
> +uint64_t raft_get_election_timer(const struct raft *);
> +
> #endif /* lib/raft.h */
> diff --git a/ovsdb/storage.c b/ovsdb/storage.c
> index d727b1eac..58018fe6d 100644
> --- a/ovsdb/storage.c
> +++ b/ovsdb/storage.c
> @@ -647,3 +647,15 @@ ovsdb_storage_peek_last_eid(struct ovsdb_storage *storage)
> }
> return raft_current_eid(storage->raft);
> }
> +
> +uint64_t
> +ovsdb_storage_max_processing_time(struct ovsdb_storage *storage)
Can it be 'const struct ovsdb_storage *storage' ?
> +{
> + if (!storage->raft) {
> + return UINT64_MAX;
> + }
> + if (raft_get_election_timer(storage->raft) > 2) {
> + return raft_get_election_timer(storage->raft) / 2;
> + }
> + return 1;
> +}
> diff --git a/ovsdb/storage.h b/ovsdb/storage.h
> index e120094d7..a8a02e0bd 100644
> --- a/ovsdb/storage.h
> +++ b/ovsdb/storage.h
> @@ -97,4 +97,6 @@ struct ovsdb_schema *ovsdb_storage_read_schema(struct ovsdb_storage *);
>
> const struct uuid *ovsdb_storage_peek_last_eid(struct ovsdb_storage *);
>
> +uint64_t ovsdb_storage_max_processing_time(struct ovsdb_storage *);
> +
> #endif /* ovsdb/storage.h */
>
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