From: Esben Nielsen <simlo@phys.au.dk>
To: Bill Huey <billh@gnuppy.monkey.org>
Cc: Ingo Molnar <mingo@elte.hu>, Steven Rostedt <rostedt@goodmis.org>,
david singleton <dsingleton@mvista.com>,
<linux-kernel@vger.kernel.org>
Subject: Re: RT Mutex patch and tester [PREEMPT_RT]
Date: Fri, 13 Jan 2006 09:47:39 +0100 (MET) [thread overview]
Message-ID: <Pine.LNX.4.44L0.0601130937540.9269-100000@lifa01.phys.au.dk> (raw)
In-Reply-To: <20060113080734.GA22091@gnuppy.monkey.org>
On Fri, 13 Jan 2006, Bill Huey wrote:
> On Thu, Jan 12, 2006 at 01:54:23PM +0100, Esben Nielsen wrote:
> > turnstiles? What is that?
>
> http://www.freebsd.org/cgi/cvsweb.cgi/src/sys/kern/subr_turnstile.c
>
> Please, read. Now tell me or not if that looks familiar ? :)
Yes, it reminds me of Ingo's first approach to pi locking:
Everything is done under a global spin lock. In Ingo's approach it was the
pi_lock. In turnstiles it is sched_lock, which (without looking at other
code in FreeBSD) locks the whole scheduler.
Although making the code a lot simpler, scalability is ofcourse the main
issue here. But apparently FreeBSD does have a global lock protecting the
scheduler anyway.
Otherwise it looks a lot like the rt_mutex.
Esben
>
> Moving closer an implementation is arguable, but it is something that
> should be considered somewhat since folks in both the Solaris (and
> FreeBSD) communities have given a lot more consideration to these issues.
>
> The stack allocated objects are fine for now. Priority inheritance
> chains should never get long with a fine grained kernel, so the use
> of a stack allocated object and migrating pi-ed waiters should not
> be a major real world issue in Linux yet.
>
> Folks should also consider using an adaptive spin in the __grab_lock() (sp?)
> related loops as a possible way of optimizing away the immediate blocks.
> FreeBSD actually checks the owner of a lock aacross another processor
> to see if it's actively running, "current", and will block or wait if
> it's running or not respectively. It's pretty trivial code, so it's
> not a big issue to implement. This is ignoring the CPU local storage
> issues.
>
> bill
>
> -
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next prev parent reply other threads:[~2006-01-13 8:51 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-01-11 17:25 RT Mutex patch and tester [PREEMPT_RT] Esben Nielsen
2006-01-11 17:51 ` Steven Rostedt
2006-01-11 21:45 ` Esben Nielsen
2006-01-12 11:33 ` Bill Huey
2006-01-12 12:54 ` Esben Nielsen
2006-01-13 8:07 ` Bill Huey
2006-01-13 8:47 ` Esben Nielsen [this message]
2006-01-13 10:19 ` Bill Huey
2006-01-15 4:24 ` Bill Huey
2006-01-16 8:35 ` Esben Nielsen
2006-01-16 10:22 ` Bill Huey
2006-01-16 10:53 ` Bill Huey
2006-01-16 11:30 ` Esben Nielsen
[not found] ` <Pine.LNX.4.44L0.0601181120100.1993-201000@lifa02.phys.au.dk>
2006-01-18 10:38 ` Ingo Molnar
2006-01-18 12:49 ` Steven Rostedt
2006-01-18 14:18 ` Esben Nielsen
[not found] ` <Pine.LNX.4.44L0.0601230047290.31387-201000@lifa01.phys.au.dk>
2006-01-23 0:38 ` david singleton
2006-01-23 2:04 ` Bill Huey
2006-01-23 9:33 ` Esben Nielsen
2006-01-23 14:23 ` Steven Rostedt
2006-01-23 15:14 ` Esben Nielsen
2006-01-27 15:18 ` Esben Nielsen
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