Date: Wed, 23 Mar 2005 07:37:27 +0100
From: Ingo Molnar <mingo@elte.hu>
To: "Paul E. McKenney" <paulmck@us.ibm.com>
Cc: linux-kernel@vger.kernel.org, Esben Nielsen <simlo@phys.au.dk>
Subject: Re: [patch] Real-Time Preemption, -RT-2.6.12-rc1-V0.7.41-07
Message-ID: <20050323063727.GA32199@elte.hu>
References: <20050321090122.GA8066@elte.hu> <20050321090622.GA8430@elte.hu> <20050322054345.GB1296@us.ibm.com> <20050322072413.GA6149@elte.hu> <20050322092331.GA21465@elte.hu> <20050322093201.GA21945@elte.hu> <20050322100153.GA23143@elte.hu> <20050322112856.GA25129@elte.hu> <20050323061601.GE1294@us.ibm.com> <20050323063317.GB31626@elte.hu>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20050323063317.GB31626@elte.hu>
User-Agent: Mutt/1.4.1i
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1077
Lines: 23


* Ingo Molnar <mingo@elte.hu> wrote:

> the 'migrate read count' solution seems more promising, as it would
> keep other parts of the RCU code unchanged. [ But it seems to break
> the nice 'flip pointers' method you found to force a grace period. If
> a 'read section' can migrate from one CPU to another then it can
> migrate back as well, at which point it cannot have the 'old' pointer.
> Maybe it would still work better than no flip pointers. ]

the flip pointer method could be made to work if we had a NR_CPUS array
of 'current RCU pointer' values attached to the task - and that array
would be cleared if the task exits the read section. But this has memory
usage worries with large NR_CPUS. (full clearing of the array can be
avoided by using some sort of 'read section generation' counter attached
to each pointer)

	Ingo
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/