lkml.org 
[lkml]   [2006]   [Sep]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [PATCH] move put_task_struct() reaping into a thread [Re: 2.6.18-rt1]
Date
Ingo Molnar <mingo@elte.hu> writes:

> * Eric W. Biederman <ebiederm@xmission.com> wrote:
>
>> Yes I am. The motivator would be the RT work but I don't see a reason
>> why the it couldn't be put in the mainline kernel. If not at least we
>> need the big fat comment in the mainline kernel that says
>> put_task_struct must be safe to call with interrupts disabled.
>>
>> The way the code is structured now it deviates from the mainline
>> kernel in more than just changing locking behavior. Which is what
>> brought me into this conversation in the first place. So removing
>> that point of discord would be good.
>
> well, this is one of those few cases (out of ~50,000 lock uses in the
> kernel) where such a change was unavoidable: put_task_struct() is used
> in the scheduler context-switch path. (see sched.c:finish_task_switch())

I had missed that was in a preempt disable path when I skimmed through
the users.

> So that's why i first turned it into a separate, extra delayed-free via
> the "desched thread", and later on picked up the RCUification from Paul
> McKenney. The RCUification was the simpler (and hence easier to
> maintain) change. There is no problem with putting this into the RCU
> path on PREEMPT_RT, as this is a resource-freeing act. I.e. whatever
> 'delay' there might be in RCU processing, it does not impact program
> logic. I agree with you that on !PREEMPT_RT there's no reason to
> complicate things with an extra layer of indirection.

I'm still wondering if we can move put_task_struct a little lower in
the logic in the places where it is called, so it isn't called under a
lock, or with preemption disabled. The only downside I see is that it
might convolute the logic into unreadability.

In general I get nervous about calling big functions while holding locks.

Eric
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2006-09-27 16:05    [from the cache]
©2003-2014 Jasper Spaans. Advertise on this site