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Date: Thu, 29 Mar 2007 22:06:41 -0400
From: "Lee Revell" <rlrevell@joe-job.com>
To: "Davide Libenzi" <davidel@xmailserver.org>
Subject: Re: [patch] queued spinlocks (i386)
Cc: "Oleg Nesterov" <oleg@tv-sign.ru>, "Nick Piggin" <npiggin@suse.de>,
       "Ravikiran G Thirumalai" <kiran@scalex86.org>,
       "Ingo Molnar" <mingo@elte.hu>, "Nikita Danilov" <nikita@clusterfs.com>,
       "Andrew Morton" <akpm@linux-foundation.org>,
       "Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>
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On 3/29/07, Davide Libenzi <davidel@xmailserver.org> wrote:
> On Thu, 29 Mar 2007, Oleg Nesterov wrote:
>
> > On 03/28, Nick Piggin wrote:
> > >
> > > Well with my queued spinlocks, all that lockbreak stuff can just come out
> > > of the spin_lock, break_lock out of the spinlock structure, and
> > > need_lockbreak just becomes (lock->qhead - lock->qtail > 1).
> >
> > Q: queued spinlocks are not CONFIG_PREEMPT friendly,
>
> Why? Is CONFIG_PREEMPT friendly to anyone? :)

Until someone fixes all the places in the kernel where scheduling can
be held off for tens of milliseconds, CONFIG_PREEMPT will be an
absolute requirement for many applications like audio and gaming.

Many of these were fixed a while back during early -rt development but
at some point the process stalled as the remaining cases were too hard
to fix...

Lee