From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Manfred Spraul <manfred@colorfullife.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
Andrew Morton <akpm@google.com>,
Thomas Gleixner <tglx@linutronix.de>,
Mike Galbraith <efault@gmx.de>
Subject: Re: [PATCH 5/5] ipc/sem.c: alternatives to preempt_disable()
Date: Tue, 24 Jan 2012 15:51:45 +0100 [thread overview]
Message-ID: <1327416705.2446.58.camel@twins> (raw)
In-Reply-To: <1318684920-2033-1-git-send-email-manfred@colorfullife.com>
On Sat, 2011-10-15 at 15:22 +0200, Manfred Spraul wrote:
> ipc/sem.c uses a custom wakeup scheme that relies on preempt_disable().
> On -RT, this causes increased latencies and debug warnings.
>
> The patch adds two additional schemes:
> - one built around a completion - could be better for -RT kernels
> - one built around a spinlock - unfortunately it's broken
> - and the current one
>
> Mike, Peter: Would the completion work on -rt?
>
> My preferred solution would be the spinlock implementation:
> RT would use premptible spinlocks, mainline normal spinlocks.
> Thus both get the optimal implementation without any special code in
> ipc/sem.c.
> Unfortunately, I don't see how it could be fixed.
Sorry, I was convinced I replied to this, but I cannot actually find
anything in my send folder or elsewhere. Thanks for poking Andrew.
Yes I think it should work, and I'm afraid I have to agree with not
being able to make the spinlock thing work properly. Even if you were to
use arch_spin_* primitives you can still run into the 256 limit --
although not from the preempt_count in that case. Nor would arch_spin_
do what we need on -rt.
next prev parent reply other threads:[~2012-01-24 14:51 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-10-15 13:22 [PATCH 5/5] ipc/sem.c: alternatives to preempt_disable() Manfred Spraul
2012-01-24 14:51 ` Peter Zijlstra [this message]
2012-01-28 19:01 ` Manfred Spraul
2012-03-28 23:06 ` Andrew Morton
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