linux-kernel - Re: [patch] queued spinlocks (i386)

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Date:	Thu, 29 Mar 2007 22:06:41 -0400
From:	"Lee Revell" <rlrevell@...-job.com>
To:	"Davide Libenzi" <davidel@...ilserver.org>
Cc:	"Oleg Nesterov" <oleg@...sign.ru>, "Nick Piggin" <npiggin@...e.de>,
	"Ravikiran G Thirumalai" <kiran@...lex86.org>,
	"Ingo Molnar" <mingo@...e.hu>,
	"Nikita Danilov" <nikita@...sterfs.com>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>
Subject: Re: [patch] queued spinlocks (i386)

On 3/29/07, Davide Libenzi <davidel@...ilserver.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
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