I'm wondering if it'd be cleaner to have ukey_create() return a locked
ukey, and to pull the try_lock() into the critical section for the
ukeys map? I.E.
lock_hmap()
ukey = ukey_lookup()
if (!ukey) {
//create and insert
} else {
// trylock
}
unlock_hmap()
What do you think?
On Thu, May 29, 2014 at 6:38 PM, Joe Stringer <[email protected]> wrote:
> This patch refactors the code around ukey creation and lookup to
> simplify the code for callers. A new function ukey_acquire() combines
> these functions and attempts to acquire a lock on the ukey. Failure to
> acquire a lock on the ukey is usually a sign that another thread is
> handling the same flow concurrently, which means the flow does not need
> to be handled anyway.
>
> Signed-off-by: Joe Stringer <[email protected]>
> ---
> ofproto/ofproto-dpif-upcall.c | 86
> ++++++++++++++++++-----------------------
> 1 file changed, 37 insertions(+), 49 deletions(-)
>
> diff --git a/ofproto/ofproto-dpif-upcall.c b/ofproto/ofproto-dpif-upcall.c
> index 1c82b6b..36e9d41 100644
> --- a/ofproto/ofproto-dpif-upcall.c
> +++ b/ofproto/ofproto-dpif-upcall.c
> @@ -216,6 +216,12 @@ static void upcall_unixctl_set_flow_limit(struct
> unixctl_conn *conn, int argc,
>
> static struct udpif_key *ukey_create(const struct nlattr *key, size_t
> key_len,
> long long int used);
> +static struct udpif_key *ukey_lookup(struct udpif *udpif,
> + const struct nlattr *key, size_t
> key_len,
> + uint32_t hash);
> +static bool ukey_acquire(struct udpif *udpif, const struct nlattr *key,
> + size_t key_len, long long int used,
> + struct udpif_key **result);
> static void ukey_delete(struct revalidator *, struct udpif_key *);
>
> static atomic_bool enable_megaflows = ATOMIC_VAR_INIT(true);
> @@ -983,8 +989,9 @@ handle_upcalls(struct handler *handler, struct upcall
> *upcalls,
>
> /* Must be called with udpif->ukeys[hash % udpif->n_revalidators].mutex. */
> static struct udpif_key *
> -ukey_lookup__(struct udpif *udpif, const struct nlattr *key, size_t key_len,
> - uint32_t hash)
> +ukey_lookup(struct udpif *udpif, const struct nlattr *key, size_t key_len,
> + uint32_t hash)
> + OVS_REQUIRES(udpif->ukeys->mutex)
> {
> struct udpif_key *ukey;
> struct hmap *hmap = &udpif->ukeys[hash % udpif->n_revalidators].hmap;
> @@ -998,21 +1005,8 @@ ukey_lookup__(struct udpif *udpif, const struct nlattr
> *key, size_t key_len,
> }
>
> static struct udpif_key *
> -ukey_lookup(struct udpif *udpif, const struct nlattr *key, size_t key_len,
> - uint32_t hash)
> -{
> - struct udpif_key *ukey;
> - uint32_t idx = hash % udpif->n_revalidators;
> -
> - ovs_mutex_lock(&udpif->ukeys[idx].mutex);
> - ukey = ukey_lookup__(udpif, key, key_len, hash);
> - ovs_mutex_unlock(&udpif->ukeys[idx].mutex);
> -
> - return ukey;
> -}
> -
> -static struct udpif_key *
> ukey_create(const struct nlattr *key, size_t key_len, long long int used)
> + OVS_NO_THREAD_SAFETY_ANALYSIS
> {
> struct udpif_key *ukey = xmalloc(sizeof *ukey);
> ovs_mutex_init(&ukey->mutex);
> @@ -1020,38 +1014,47 @@ ukey_create(const struct nlattr *key, size_t key_len,
> long long int used)
> ukey->key = (struct nlattr *) &ukey->key_buf;
> memcpy(&ukey->key_buf, key, key_len);
> ukey->key_len = key_len;
> -
> - ovs_mutex_lock(&ukey->mutex);
> ukey->mark = false;
> ukey->flow_exists = true;
> ukey->created = used ? used : time_msec();
> memset(&ukey->stats, 0, sizeof ukey->stats);
> ukey->xcache = NULL;
> - ovs_mutex_unlock(&ukey->mutex);
>
> return ukey;
> }
>
> -/* Checks for a ukey in 'udpif->ukeys' with the same 'ukey->key' and 'hash',
> - * and inserts 'ukey' if it does not exist.
> +/* Searches for a ukey in 'udpif->ukeys' that matches 'key' and 'key_len' and
> + * attempts to lock the ukey. If the ukey does not exist, create it.
> *
> - * Returns true if 'ukey' was inserted into 'udpif->ukeys', false otherwise.
> */
> + * Returns true on success, setting *result to the matching ukey and
> returning
> + * it in a locked state. Otherwise, returns false and clears *result. */
> static bool
> -udpif_insert_ukey(struct udpif *udpif, struct udpif_key *ukey, uint32_t hash)
> +ukey_acquire(struct udpif *udpif, const struct nlattr *key, size_t key_len,
> + long long int used, struct udpif_key **result)
> + OVS_TRY_LOCK(true, (*result)->mutex)
> {
> - struct udpif_key *duplicate;
> - uint32_t idx = hash % udpif->n_revalidators;
> + struct udpif_key *ukey;
> + uint32_t hash, idx;
> bool ok;
>
> + hash = hash_bytes(key, key_len, udpif->secret);
> + idx = hash % udpif->n_revalidators;
> +
> ovs_mutex_lock(&udpif->ukeys[idx].mutex);
> - duplicate = ukey_lookup__(udpif, ukey->key, ukey->key_len, hash);
> - if (duplicate) {
> + ukey = ukey_lookup(udpif, key, key_len, hash);
> + if (!ukey) {
> + ukey = ukey_create(key, key_len, used);
> + hmap_insert(&udpif->ukeys[idx].hmap, &ukey->hmap_node, hash);
> + }
> + ovs_mutex_unlock(&udpif->ukeys[idx].mutex);
> +
> + if (ovs_mutex_trylock(&ukey->mutex)) {
> ok = false;
> + *result = NULL;
> } else {
> - hmap_insert(&udpif->ukeys[idx].hmap, &ukey->hmap_node, hash);
> ok = true;
> + *result = ukey;
> }
> - ovs_mutex_unlock(&udpif->ukeys[idx].mutex);
>
> return ok;
> }
> @@ -1362,28 +1365,13 @@ revalidate(struct revalidator *revalidator)
>
> for (f = flows; f < &flows[n_dumped]; f++) {
> long long int used = f->stats.used;
> - uint32_t hash = hash_bytes(f->key, f->key_len, udpif->secret);
> - struct udpif_key *ukey = ukey_lookup(udpif, f->key, f->key_len,
> - hash);
> + struct udpif_key *ukey;
> bool already_dumped, mark;
>
> - if (!ukey) {
> - ukey = ukey_create(key, key_len, used);
> - if (!udpif_insert_ukey(udpif, ukey, hash)) {
> - /* The same ukey has already been created. This means
> that
> - * another revalidator is processing this flow
> - * concurrently, so don't bother processing it. */
> - COVERAGE_INC(upcall_duplicate_flow);
> - ukey_delete(NULL, ukey);
> - continue;
> - }
> - }
> -
> - if (ovs_mutex_trylock(&ukey->mutex)) {
> - /* The flow has been dumped, and is being handled by another
> - * revalidator concurrently. This can occasionally occur if
> the
> - * datapath is changed in the middle of a flow dump. Rather
> than
> - * perform the same work twice, skip the flow this time. */
> + if (!ukey_acquire(udpif, f->key, f->key_len, used, &ukey)) {
> + /* We couldn't acquire the ukey. This means that
> + * another revalidator is processing this flow
> + * concurrently, so don't bother processing it. */
> COVERAGE_INC(upcall_duplicate_flow);
> continue;
> }
> --
> 1.7.10.4
>
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