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SubjectRe: [PATCH 11/17] staging: lustre: ptlrpc: use workqueue for pinger
On Thu, Mar 08 2018, Dilger, Andreas wrote:

> On Mar 1, 2018, at 16:31, NeilBrown <neilb@suse.com> wrote:
>>
>> lustre has a "Pinger" kthread which periodically pings peers
>> to ensure all hosts are functioning.
>>
>> This can more easily be done using a work queue.
>>
>> As maintaining contact with other peers is import for
>> keeping the filesystem running, and as the filesystem might
>> be involved in freeing memory, it is safest to have a
>> separate WQ_MEM_RECLAIM workqueue.
>>
>> The SVC_EVENT functionality to wake up the thread can be
>> replaced with mod_delayed_work().
>>
>> Also use round_jiffies_up_relative() rather than setting a
>> minimum of 1 second delay. The PING_INTERVAL is measured in
>> seconds so this meets the need is allow the workqueue to
>> keep wakeups synchronized.
>>
>> Signed-off-by: NeilBrown <neilb@suse.com>
>
> Looks reasonable. Fortunately, pinging the server does not need
> to be very accurate since it is only done occasionally when the
> client is otherwise idle, so it shouldn't matter if the workqueue
> operation is delayed by a few seconds.
>
> Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>

Thanks a lot for the thorough review!
The above implies that we don't need WQ_MEM_RECLAIM. I didn't dig in to
exactly when and why pings happened so I thought having WQ_MEM_RECLAIM
we safest. If pings only happen when the client is otherwise idle, the
it isn't needed. I'll remove it.

Thanks,
NeilBrown


>
>> ---
>> drivers/staging/lustre/lustre/ptlrpc/pinger.c | 81 +++++++------------------
>> 1 file changed, 24 insertions(+), 57 deletions(-)
>>
>> diff --git a/drivers/staging/lustre/lustre/ptlrpc/pinger.c b/drivers/staging/lustre/lustre/ptlrpc/pinger.c
>> index b5f3cfee8e75..0775b7a048bb 100644
>> --- a/drivers/staging/lustre/lustre/ptlrpc/pinger.c
>> +++ b/drivers/staging/lustre/lustre/ptlrpc/pinger.c
>> @@ -217,21 +217,18 @@ static void ptlrpc_pinger_process_import(struct obd_import *imp,
>> }
>> }
>>
>> -static int ptlrpc_pinger_main(void *arg)
>> -{
>> - struct ptlrpc_thread *thread = arg;
>> -
>> - /* Record that the thread is running */
>> - thread_set_flags(thread, SVC_RUNNING);
>> - wake_up(&thread->t_ctl_waitq);
>> +static struct workqueue_struct *pinger_wq;
>> +static void ptlrpc_pinger_main(struct work_struct *ws);
>> +static DECLARE_DELAYED_WORK(ping_work, ptlrpc_pinger_main);
>>
>> - /* And now, loop forever, pinging as needed. */
>> - while (1) {
>> - unsigned long this_ping = cfs_time_current();
>> - long time_to_next_wake;
>> - struct timeout_item *item;
>> - struct obd_import *imp;
>> +static void ptlrpc_pinger_main(struct work_struct *ws)
>> +{
>> + unsigned long this_ping = cfs_time_current();
>> + long time_to_next_wake;
>> + struct timeout_item *item;
>> + struct obd_import *imp;
>>
>> + do {
>> mutex_lock(&pinger_mutex);
>> list_for_each_entry(item, &timeout_list, ti_chain) {
>> item->ti_cb(item, item->ti_cb_data);
>> @@ -260,50 +257,24 @@ static int ptlrpc_pinger_main(void *arg)
>> time_to_next_wake,
>> cfs_time_add(this_ping,
>> PING_INTERVAL * HZ));
>> - if (time_to_next_wake > 0) {
>> - wait_event_idle_timeout(thread->t_ctl_waitq,
>> - thread_is_stopping(thread) ||
>> - thread_is_event(thread),
>> - max_t(long, time_to_next_wake, HZ));
>> - if (thread_test_and_clear_flags(thread, SVC_STOPPING))
>> - break;
>> - /* woken after adding import to reset timer */
>> - thread_test_and_clear_flags(thread, SVC_EVENT);
>> - }
>> - }
>> + } while (time_to_next_wake <= 0);
>>
>> - thread_set_flags(thread, SVC_STOPPED);
>> - wake_up(&thread->t_ctl_waitq);
>> -
>> - CDEBUG(D_NET, "pinger thread exiting, process %d\n", current_pid());
>> - return 0;
>> + queue_delayed_work(pinger_wq, &ping_work,
>> + round_jiffies_up_relative(time_to_next_wake));
>> }
>>
>> -static struct ptlrpc_thread pinger_thread;
>> -
>> int ptlrpc_start_pinger(void)
>> {
>> - struct task_struct *task;
>> - int rc;
>> -
>> - if (!thread_is_init(&pinger_thread) &&
>> - !thread_is_stopped(&pinger_thread))
>> + if (pinger_wq)
>> return -EALREADY;
>>
>> - init_waitqueue_head(&pinger_thread.t_ctl_waitq);
>> -
>> - strcpy(pinger_thread.t_name, "ll_ping");
>> -
>> - task = kthread_run(ptlrpc_pinger_main, &pinger_thread,
>> - pinger_thread.t_name);
>> - if (IS_ERR(task)) {
>> - rc = PTR_ERR(task);
>> - CERROR("cannot start pinger thread: rc = %d\n", rc);
>> - return rc;
>> + pinger_wq = alloc_workqueue("ptlrpc_pinger", WQ_MEM_RECLAIM, 1);
>> + if (!pinger_wq) {
>> + CERROR("cannot start pinger workqueue\n");
>> + return -ENOMEM;
>> }
>> - wait_event_idle(pinger_thread.t_ctl_waitq,
>> - thread_is_running(&pinger_thread));
>>
>> + queue_delayed_work(pinger_wq, &ping_work, 0);
>> return 0;
>> }
>>
>> @@ -313,16 +284,13 @@ int ptlrpc_stop_pinger(void)
>> {
>> int rc = 0;
>>
>> - if (thread_is_init(&pinger_thread) ||
>> - thread_is_stopped(&pinger_thread))
>> + if (!pinger_wq)
>> return -EALREADY;
>>
>> ptlrpc_pinger_remove_timeouts();
>> - thread_set_flags(&pinger_thread, SVC_STOPPING);
>> - wake_up(&pinger_thread.t_ctl_waitq);
>> -
>> - wait_event_idle(pinger_thread.t_ctl_waitq,
>> - thread_is_stopped(&pinger_thread));
>> + cancel_delayed_work_sync(&ping_work);
>> + destroy_workqueue(pinger_wq);
>> + pinger_wq = NULL;
>>
>> return rc;
>> }
>> @@ -505,6 +473,5 @@ static int ptlrpc_pinger_remove_timeouts(void)
>>
>> void ptlrpc_pinger_wake_up(void)
>> {
>> - thread_add_flags(&pinger_thread, SVC_EVENT);
>> - wake_up(&pinger_thread.t_ctl_waitq);
>> + mod_delayed_work(pinger_wq, &ping_work, 0);
>> }
>>
>>
>
> Cheers, Andreas
> --
> Andreas Dilger
> Lustre Principal Architect
> Intel Corporation
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