[haiku-gsoc] Re: [HCD]: Bfs bug #1

2008/6/21 Ingo Weinhold <ingo_weinhold@xxxxxx>:
>
> On 2008-06-20 at 22:08:03 [+0200], Salvatore Benedetto <emitrax@xxxxxxxxx>
> wrote:
>> 2008/6/19 Ingo Weinhold <ingo_weinhold@xxxxxx>:
>> >
>> > I think, if at all, it's more likely a problem of the ide module or
>> > related
>> > modules. It normally shouldn't take more than 10 seconds to write back
>> > changes to a file. Well unless the file is quite big and there are a lot
>> > of
>> > cache changes... or the system doesn't have an I/O scheduler and starts
>> > thrashing the disk in low-memory situations. So maybe nothing really goes
>> > wrong after all; at least nothing that wouldn't be fixed by using a
>> > condition variable and wait indefinitely. You could try increasing the
>> > timeout in get_vnode() (maybe to a minute?) and see if the problem still
>> > occurs.
>>
>> I increased the timeout and the problem persist. Same stack, same threads.
>
> Well, then it's supposedly a problem in the IDE module.

I'm sure about this. I've run the same test again, and realized that
the low memory thread,
in one case, was actually in the run_queue with a priority of 5 (LOW),
but couldn't get scheduled because
the tar application, which run continuosly and has a greater priority
(10 - NORMAL).

I changed the priority of the thread (low memory) to NORMAL + 1, to
see if something different would happened, and it
actually crashed with a different stack trace, but the problem is
still the same. Page writer waits for a node
kept busy by the low memory thread.

Now, I know our scheduler is not the best one, so I wouldn't exclude a
"starvation" problem, since the tar
application keeps running, eating all the CPU making the system
unusable (Yep, we still need a scheduler btw!).

I'm going to run another test with a greater priority for the lower thread.

One question though, is it possible to see who is holding a semaphore?
That is, not who created it,
but who is holding it, because I haven't understand if the attached
screenshot shows a deadlock or not.

Regards,
-- 
Salvatore Benedetto (a.k.a. emitrax)
Student of Computer Engineer
University of Pisa
www.haiku-os.it

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