[OpenAFS-devel] dealing with rxevent queue stalls

[Mark Vitale]

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On Sep 24, 2013, at 8:54 AM, Jeffrey Altman =
<jaltman@your-file-system.com> wrote:

> On 9/23/2013 3:52 PM, Mark Vitale wrote:
>> 2) Volume releases suffer from poor performance and occasionally fail =
with timeouts.
>>  - root cause was heavier-than-normal vlserver load (perhaps caused =
by disk performance slowdowns); this starved LWP IOMGR, which in turn =
prevented LWP rx_Listener from being dispatched (priority inversion), =
leading to a grossly delayed rxevent queue.
>=20
> Did you intend to write "rx_Listener" in the above sentence or did you
> mean the rx_Event thread? =20
In the LWP case I did mean to type rx_Listener, which is the "name" of =
the LWP.  In LWP, there are not separate threads for listener and event =
handler logic; they run alternately in the same (listener) thread. The =
actual code it runs is rx_ListenerProc() -> rxi_ListenerProc(), which =
loops and alternately calls rxevent_RaiseEvents() and IOMGR_Select().  =
In this case the high-priority listener thread is blocked on =
IOMGR_Select(), which is blocked on the low priority IOMGR thread to be =
dispatched, which in turn is blocked by medium priority worker threads.  =
In this situation, rxevent_RaiseEvents() will never
be invoked until ALL the worker threads are no longer runnable.

--
Mark Vitale
mvitale@sinenomine.net


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