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Message-ID: <alpine.DEB.1.10.0809081056530.23508@gandalf.stny.rr.com>
Date: Mon, 8 Sep 2008 11:04:31 -0400 (EDT)
From: Steven Rostedt <rostedt@...dmis.org>
To: Sujit Karataparambil <sjt.kar@...il.com>
cc: linux-rt-users <linux-rt-users@...r.kernel.org>,
xavier droubay <xavier.droubay@...il.com>,
Chirag Jog <chirag@...ux.vnet.ibm.com>,
Thomas Gleixner <tglx@...utronix.de>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Convert tlbstate_lock spin_lock to raw_spin_lock
[ Refrain from using "unlisted-recipients" please! ]
On Mon, 8 Sep 2008, Sujit Karataparambil wrote:
> Chirag,
>
> Kindly understand what xavier is trying to do. He is Trying to disable smp.
> The RT - Linux Code is dependent on the mutex lock to perform some
> soft/hard real time processing. This is an problem with the mutex lock.
It is not a problem with the mutex lock.
>
> Kindly check with some one before signing off patches.
The patch is legit.
The problem is simply that functions like flush_tlb_current_task and
flush_tlb_mm disable preemption and then call flush_tlb_others.
This function locks the tlbstate_lock which is currently a rtmutex. An
rtmutex can not be called with preemption disabled. The tlbstate_lock is
static, small and confined. I'm not sure we can change this code (flushing
the TLB) in a way where we can allow preemption. This may just be a
latency that we must hit.
-- Steve
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