From: Esben Nielsen <simlo@phys.au.dk>
To: Ingo Molnar <mingo@elte.hu>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>,
dipankar@in.ibm.com, shemminger@osdl.org, akpm@osdl.org,
torvalds@osdl.org, rusty@au1.ibm.com, tgall@us.ibm.com,
jim.houston@comcast.net, manfred@colorfullife.com, gh@us.ibm.com,
linux-kernel@vger.kernel.org
Subject: Re: Real-Time Preemption and RCU
Date: Tue, 22 Mar 2005 11:19:58 +0100 (MET) [thread overview]
Message-ID: <Pine.OSF.4.05.10503221102200.25802-100000@da410.phys.au.dk> (raw)
In-Reply-To: <20050322092032.GA20240@elte.hu>
On Tue, 22 Mar 2005, Ingo Molnar wrote:
>
> * Esben Nielsen <simlo@phys.au.dk> wrote:
>
> > On the other hand with a rw-lock being unlimited - and thus do not
> > keep track of it readers - the readers can't be boosted by the writer.
> > Then you are back to square 1: The grace period can take a very long
> > time.
>
> btw., is the 'very long grace period' a real issue? We could avoid all
> the RCU read-side locking latencies by making it truly unlocked and just
> living with the long grace periods. Perhaps it's enough to add an
> emergency mechanism to the OOM handler, which frees up all the 'blocked
> by preemption' RCU callbacks via some scheduler magic. (e.g. such an
> emergency mechanism could be _conditional_ locking on the read side -
> i.e. new RCU read-side users would be blocked until the OOM situation
> goes away, or something like that.)
You wont catch RCU read-sides already entered - see below.
>
> your patch is implementing just that, correct? Would you mind redoing it
> against a recent -RT base? (-40-04 or so)
>
In fact I am working on clean 2.6.12-rc1 right now. I figured this is
orthorgonal to the rest RT patch and can probably go upstream immediately.
Seemed to work. I'll try to make into a clean patch soonish and also try
it on -40-04.
I am trying to make a boosting mechanism in the scheduler such that RCU
readers are boosted to MAX_RT_PRIO when preempted. I have to take it out
first.
Any specific tests I have to run? I am considering making an RCU test
device.
> also, what would be the worst-case workload causing long grace periods?
A nice 19 task, A, enter an RCU region and is preempted. A lot of other
tasks starts running. Then task A might starved for _minuttes_ such that
there is no RCU-grace periods in all that time.
>
> Ingo
Esben
next prev parent reply other threads:[~2005-03-22 10:20 UTC|newest]
Thread overview: 58+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-03-18 0:20 Real-Time Preemption and RCU Paul E. McKenney
2005-03-18 7:49 ` Ingo Molnar
2005-03-18 16:43 ` Paul E. McKenney
2005-03-18 17:11 ` Ingo Molnar
2005-03-18 17:29 ` Paul E. McKenney
2005-03-18 20:35 ` Paul E. McKenney
2005-03-18 22:22 ` Paul E. McKenney
2005-03-19 0:48 ` Paul E. McKenney
2005-03-18 8:44 ` Ingo Molnar
2005-03-18 9:04 ` Ingo Molnar
2005-03-18 9:38 ` Ingo Molnar
2005-03-18 9:13 ` Ingo Molnar
2005-03-18 9:28 ` Ingo Molnar
2005-03-18 9:53 ` Ingo Molnar
2005-03-18 15:33 ` Paul E. McKenney
2005-03-19 5:03 ` Manfred Spraul
2005-03-19 16:26 ` Ingo Molnar
2005-03-20 6:36 ` Manfred Spraul
2005-03-20 9:25 ` Thomas Gleixner
2005-03-20 16:57 ` Manfred Spraul
2005-03-20 21:38 ` Bill Huey
2005-03-20 21:59 ` Bill Huey
2005-03-18 10:03 ` Ingo Molnar
2005-03-18 11:30 ` Ingo Molnar
2005-03-18 16:48 ` Esben Nielsen
2005-03-18 17:19 ` Ingo Molnar
2005-03-20 13:29 ` Esben Nielsen
2005-03-20 22:38 ` Paul E. McKenney
2005-03-20 23:23 ` Esben Nielsen
2005-03-22 5:53 ` Paul E. McKenney
2005-03-22 8:55 ` Esben Nielsen
2005-03-22 9:20 ` Ingo Molnar
2005-03-22 10:19 ` Esben Nielsen [this message]
2005-03-23 5:40 ` Paul E. McKenney
2005-03-23 11:44 ` Esben Nielsen
2005-03-24 7:02 ` Paul E. McKenney
2005-03-22 10:56 ` Ingo Molnar
2005-03-22 11:39 ` Esben Nielsen
2005-03-22 13:10 ` Ingo Molnar
2005-03-22 15:08 ` Esben Nielsen
2005-03-18 15:48 ` Paul E. McKenney
2005-03-18 11:38 ` Ingo Molnar
2005-03-18 12:56 ` Bill Huey
2005-03-18 13:17 ` Bill Huey
2005-03-18 15:57 ` Paul E. McKenney
2005-03-18 16:02 ` Ingo Molnar
2005-03-18 16:55 ` Esben Nielsen
2005-03-22 10:04 ` Bill Huey
2005-03-22 10:17 ` Bill Huey
2005-03-22 10:34 ` Bill Huey
2005-03-22 10:38 ` Esben Nielsen
2005-03-18 22:26 ` Herbert Xu
2005-03-19 16:31 ` Ingo Molnar
2005-03-20 8:01 ` Kyle Moffett
2005-03-22 8:08 ` Ingo Molnar
2005-03-18 15:54 ` Paul E. McKenney
2005-03-18 15:58 ` Ingo Molnar
2009-06-11 22:57 real-time preemption " James Huang
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