kernel/linux.git/include/linux/sunrpc/svc.h, branch v6.7.3

NFSD: add rpc_status netlink support

2023-10-16T16:44:09+00:00

Introduce rpc_status netlink support for NFSD in order to dump pending RPC requests debugging information from userspace. Closes: https://bugzilla.linux-nfs.org/show_bug.cgi?id=366 Tested-by: Jeff Layton Signed-off-by: Lorenzo Bianconi Signed-off-by: Chuck Lever

SUNRPC: change the back-channel queue to lwq

2023-10-16T16:44:08+00:00

This removes the need to store and update back-links in the list. It also remove the need for the _bh version of spin_lock(). Signed-off-by: NeilBrown Cc: Trond Myklebust Cc: Anna Schumaker Signed-off-by: Chuck Lever

SUNRPC: discard sp_lock

2023-10-16T16:44:08+00:00

sp_lock is now only used to protect sp_all_threads. This isn't needed as sp_all_threads is only manipulated through svc_set_num_threads(), which is already serialized. Read-acccess only requires rcu_read_lock(). So no more locking is needed. Signed-off-by: NeilBrown Signed-off-by: Chuck Lever

SUNRPC: change sp_nrthreads to atomic_t

2023-10-16T16:44:07+00:00

Using an atomic_t avoids the need to take a spinlock (which can soon be removed). Choosing a thread to kill needs to be careful as we cannot set the "die now" bit atomically with the test on the count. Instead we temporarily increase the count. Signed-off-by: NeilBrown Signed-off-by: Chuck Lever

SUNRPC: use lwq for sp_sockets - renamed to sp_xprts

2023-10-16T16:44:07+00:00

lwq avoids using back pointers in lists, and uses less locking. This introduces a new spinlock, but the other one will be removed in a future patch. For svc_clean_up_xprts(), we now dequeue the entire queue, walk it to remove and process the xprts that need cleaning up, then re-enqueue the remaining queue. Signed-off-by: NeilBrown Signed-off-by: Chuck Lever

SUNRPC: only have one thread waking up at a time

2023-10-16T16:44:07+00:00

Currently if several items of work become available in quick succession, that number of threads (if available) will be woken. By the time some of them wake up another thread that was already cache-warm might have come along and completed the work. Anecdotal evidence suggests as many as 15% of wakes find nothing to do once they get to the point of looking. This patch changes svc_pool_wake_idle_thread() to wake the first thread on the queue but NOT remove it. Subsequent calls will wake the same thread. Once that thread starts it will dequeue itself and after dequeueing some work to do, it will wake the next thread if there is more work ready. This results in a more orderly increase in the number of busy threads. As a bonus, this allows us to reduce locking around the idle queue. svc_pool_wake_idle_thread() no longer needs to take a lock (beyond rcu_read_lock()) as it doesn't manipulate the queue, it just looks at the first item. The thread itself can avoid locking by using the new llist_del_first_this() interface. This will safely remove the thread itself if it is the head. If it isn't the head, it will do nothing. If multiple threads call this concurrently only one will succeed. The others will do nothing, so no corruption can result. If a thread wakes up and finds that it cannot dequeue itself that means either - that it wasn't woken because it was the head of the queue. Maybe the freezer woke it. In that case it can go back to sleep (after trying to freeze of course). - some other thread found there was nothing to do very recently, and placed itself on the head of the queue in front of this thread. It must check again after placing itself there, so it can be deemed to be responsible for any pending work, and this thread can go back to sleep until woken. No code ever tests for busy threads any more. Only each thread itself cares if it is busy. So svc_thread_busy() is no longer needed. Signed-off-by: NeilBrown Signed-off-by: Chuck Lever

SUNRPC: change service idle list to be an llist

2023-10-16T16:44:05+00:00

With an llist we don't need to take a lock to add a thread to the list, though we still need a lock to remove it. That will go in the next patch. Unlike double-linked lists, a thread cannot reliably remove itself from the list. Only the first thread can be removed, and that can change asynchronously. So some care is needed. We already check if there is pending work to do, so we are unlikely to add ourselves to the idle list and then want to remove ourselves again. If we DO find something needs to be done after adding ourselves to the list, we simply wake up the first thread on the list. If that was us, we successfully removed ourselves and can continue. If it was some other thread, they will do the work that needs to be done. We can safely sleep until woken. We also remove the test on freezing() from rqst_should_sleep(). Instead we set TASK_FREEZABLE before scheduling. This makes is safe to schedule() when a freeze is pending. As we now loop waiting to be removed from the idle queue, this is a cleaner way to handle freezing. Signed-off-by: NeilBrown Signed-off-by: Chuck Lever

SUNRPC: discard SP_CONGESTED

2023-10-16T16:44:05+00:00

We can tell if a pool is congested by checking if the idle list is empty. We don't need a separate flag. Signed-off-by: NeilBrown Signed-off-by: Chuck Lever

SUNRPC: add list of idle threads

2023-10-16T16:44:04+00:00

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 Signed-off-by: Chuck Lever

SUNRPC: change how svc threads are asked to exit.

2023-10-16T16:44:04+00:00

svc threads are currently stopped using kthread_stop(). This requires identifying a specific thread. However we don't care which thread stops, just as long as one does. So instead, set a flag in the svc_pool to say that a thread needs to die, and have each thread check this flag instead of calling kthread_should_stop(). The first thread to find and clear this flag then moves towards exiting. This removes an explicit dependency on sp_all_threads which will make a future patch simpler. Signed-off-by: NeilBrown Signed-off-by: Chuck Lever