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SUNRPC: add list of idle threads
Rather than searching a list of threads to find an idle one, having a list of idle threads allows an idle thread to be found immediately. This adds some spin_lock calls which is not ideal, but as the hold-time is tiny it is still faster than searching a list. A future patch will remove them using llist.h. This involves some subtlety and so is left to a separate patch. This removes the need for the RQ_BUSY flag. The rqst is "busy" precisely when it is not on the "idle" list. Signed-off-by: NeilBrown <neilb@suse.de> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
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@ -37,6 +37,7 @@ struct svc_pool {
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struct list_head sp_sockets; /* pending sockets */
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unsigned int sp_nrthreads; /* # of threads in pool */
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struct list_head sp_all_threads; /* all server threads */
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struct list_head sp_idle_threads; /* idle server threads */
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/* statistics on pool operation */
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struct percpu_counter sp_messages_arrived;
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@ -186,6 +187,7 @@ extern u32 svc_max_payload(const struct svc_rqst *rqstp);
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*/
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struct svc_rqst {
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struct list_head rq_all; /* all threads list */
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struct list_head rq_idle; /* On the idle list */
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struct rcu_head rq_rcu_head; /* for RCU deferred kfree */
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struct svc_xprt * rq_xprt; /* transport ptr */
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@ -262,10 +264,31 @@ enum {
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RQ_SPLICE_OK, /* turned off in gss privacy to prevent
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* encrypting page cache pages */
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RQ_VICTIM, /* Have agreed to shut down */
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RQ_BUSY, /* request is busy */
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RQ_DATA, /* request has data */
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};
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/**
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* svc_thread_set_busy - mark a thread as busy
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* @rqstp: the thread which is now busy
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*
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* If rq_idle is "empty", the thread must be busy.
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*/
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static inline void svc_thread_set_busy(struct svc_rqst *rqstp)
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{
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INIT_LIST_HEAD(&rqstp->rq_idle);
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}
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/**
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* svc_thread_busy - check if a thread as busy
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* @rqstp: the thread which might be busy
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*
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* If rq_idle is "empty", the thread must be busy.
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*/
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static inline bool svc_thread_busy(struct svc_rqst *rqstp)
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{
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return list_empty(&rqstp->rq_idle);
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}
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#define SVC_NET(rqst) (rqst->rq_xprt ? rqst->rq_xprt->xpt_net : rqst->rq_bc_net)
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/*
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@ -1677,7 +1677,6 @@ DEFINE_SVCXDRBUF_EVENT(sendto);
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svc_rqst_flag(DROPME) \
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svc_rqst_flag(SPLICE_OK) \
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svc_rqst_flag(VICTIM) \
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svc_rqst_flag(BUSY) \
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svc_rqst_flag_end(DATA)
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#undef svc_rqst_flag
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@ -510,6 +510,7 @@ __svc_create(struct svc_program *prog, unsigned int bufsize, int npools,
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pool->sp_id = i;
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INIT_LIST_HEAD(&pool->sp_sockets);
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INIT_LIST_HEAD(&pool->sp_all_threads);
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INIT_LIST_HEAD(&pool->sp_idle_threads);
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spin_lock_init(&pool->sp_lock);
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percpu_counter_init(&pool->sp_messages_arrived, 0, GFP_KERNEL);
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@ -641,7 +642,7 @@ svc_rqst_alloc(struct svc_serv *serv, struct svc_pool *pool, int node)
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folio_batch_init(&rqstp->rq_fbatch);
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__set_bit(RQ_BUSY, &rqstp->rq_flags);
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svc_thread_set_busy(rqstp);
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rqstp->rq_server = serv;
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rqstp->rq_pool = pool;
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@ -702,10 +703,13 @@ void svc_pool_wake_idle_thread(struct svc_pool *pool)
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struct svc_rqst *rqstp;
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rcu_read_lock();
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list_for_each_entry_rcu(rqstp, &pool->sp_all_threads, rq_all) {
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if (test_and_set_bit(RQ_BUSY, &rqstp->rq_flags))
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continue;
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spin_lock_bh(&pool->sp_lock);
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rqstp = list_first_entry_or_null(&pool->sp_idle_threads,
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struct svc_rqst, rq_idle);
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if (rqstp)
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list_del_init(&rqstp->rq_idle);
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spin_unlock_bh(&pool->sp_lock);
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if (rqstp) {
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WRITE_ONCE(rqstp->rq_qtime, ktime_get());
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wake_up_process(rqstp->rq_task);
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rcu_read_unlock();
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@ -737,8 +737,9 @@ static void svc_rqst_wait_for_work(struct svc_rqst *rqstp)
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set_current_state(TASK_IDLE);
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smp_mb__before_atomic();
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clear_bit(SP_CONGESTED, &pool->sp_flags);
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clear_bit(RQ_BUSY, &rqstp->rq_flags);
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smp_mb__after_atomic();
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spin_lock_bh(&pool->sp_lock);
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list_add(&rqstp->rq_idle, &pool->sp_idle_threads);
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spin_unlock_bh(&pool->sp_lock);
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/* Need to check should_sleep() again after
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* setting task state in case a wakeup happened
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@ -751,8 +752,14 @@ static void svc_rqst_wait_for_work(struct svc_rqst *rqstp)
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cond_resched();
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}
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set_bit(RQ_BUSY, &rqstp->rq_flags);
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smp_mb__after_atomic();
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/* We *must* be removed from the list before we can continue.
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* If we were woken, this is already done
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*/
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if (!svc_thread_busy(rqstp)) {
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spin_lock_bh(&pool->sp_lock);
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list_del_init(&rqstp->rq_idle);
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spin_unlock_bh(&pool->sp_lock);
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}
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} else {
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cond_resched();
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}
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