[OpenAFS-devel] Help, please: rx_EnableHotThread() forgets thread IDs in pthreaded fileserver

[Rainer Toebbicke]

I would appreciate if whoever understands RX (rx.c) could comment on this:

With rx_EnableHotThread() set in the (pthread_) fileserver, under certain 
circumstances the current thread's ID (the thing set by 
pthread_setspecific(rx_thread_id_key,...) ) is changed:


if (rx_enable_hot_thread && newcallp && sq->socketp) {
...
             *tnop = sq->tno;
...


Curiously, this is a one-way change, not a swap, with two threads ending up 
with the same thread-id afterwards. I fail to see a replenishing mechanism 
which would prevent the system from evolving to a single-thread-id 
constellation over time.

Going through a number of 'mature' fileserver dumps, indeed they show a 
drastically reduced diversity of the values of 'threadID' in the various 
rxi_ServerProc stack frames -  usually 0, 1 or 2.

A quick test shows that after disabling rx_enable_hot_thread in the fileserver 
this does NOT happen, after 10 hours of reasonable traffic all thread ids are 
still represented, no duplicates.

Of course the next step is to change rx.c and SWAP the tno's - but I'm afraid 
that this code is actually executed pretty rarely and a swap might just create 
a problem that passes unnoticed for a long time.

[the per thread rx_thread_id_key (alias threadID, alias tno, alias 
h_lwpIndex()) is vital for the h_Hold() mechanism, and failed for us even with 
the recently posted patches for the housekeeping threads applied].

-- 
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
Rainer Toebbicke        http://cern.ch/~rtb         rtb@mail.cern.ch  O__
European Laboratory for Particle Physics(CERN) - Geneva, Switzerland   > |
Phone: +41 22 767 8985       Fax: +41 22 767 7155                     ( )\( )