[OpenAFS-devel] 50 second fetch-data?

[Jeffrey Altman]

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Harald Barth wrote:
>>Longer trace of all rx traffic around the time is in 
>>/afs/pdc.kth.se/home/h/haba/Public/openafs14-rx.cap.gz
>>It contrains more than one of these hickups.
> 
> 
> Sorry, I meant trace _15_:
> /afs/pdc.kth.se/home/h/haba/Public/openafs15-rx.cap.gz
> 
> It contains a bunch of ack packets with reason=delay. 
> But what is the reason for the delay? 
> 
> Frame 119,125,126 call #49 has a 
> request: fetch-status
> reply: fetch-status 
> and then the client sends a delayed ack. 
> 
> Call 2972 has a delay packet as an answer to the
> request fetch-status and the reply.
> 
> Harald.

Just some background on how Delayed Acks should work:

Delayed Acks are used to consolidate the number of ack packets
sent when there isn't any data to send in the ack direction.
There is a guarrantee that a hard ack is sent for every
rxi_HardAckRate+1 incoming rx packets.  Otherwise a delayed
ack is scheduled.

delayed acks are to be sent either when the call is ended, the
connection is destroyed, or after the rx_hardAckDelay period (100 ms)
expires.

However, delayed ack events are really only sent when the
event_handler() thread (rx_pthread.c) calls rxevent_RaiseEvents().
rxevent_RaiseEvents() will sleep for 30 seconds if there are no
scheduled events or can take a very long time to cycle through its
list if it takes a long time to process the events that are scheduled to
be completed.

In order for rxi_SendDelayedAck() to complete it must be able to
obtain the mutex on the call->lock.  If that lock is being held
by another thread, there could be long delays in the processing
of the rxevent_RaiseEvents() queue.

Jeffrey Altman

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