From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:38370)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <serge.fdrv@gmail.com>) id 1bF3kL-0004Di-8e
	for qemu-devel@nongnu.org; Mon, 20 Jun 2016 14:16:30 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <serge.fdrv@gmail.com>) id 1bF3kG-0003fU-96
	for qemu-devel@nongnu.org; Mon, 20 Jun 2016 14:16:29 -0400
Received: from mail-lf0-x243.google.com ([2a00:1450:4010:c07::243]:35507)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <serge.fdrv@gmail.com>) id 1bF3kG-0003fO-1e
	for qemu-devel@nongnu.org; Mon, 20 Jun 2016 14:16:24 -0400
Received: by mail-lf0-x243.google.com with SMTP id w130so6202942lfd.2
	for <qemu-devel@nongnu.org>; Mon, 20 Jun 2016 11:16:23 -0700 (PDT)
References: <8737o7su4z.fsf@linaro.org>
From: Sergey Fedorov <serge.fdrv@gmail.com>
Message-ID: <576832F4.5080202@gmail.com>
Date: Mon, 20 Jun 2016 21:16:20 +0300
MIME-Version: 1.0
In-Reply-To: <8737o7su4z.fsf@linaro.org>
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 8bit
Subject: Re: [Qemu-devel] [RFC 0/7] Safe watch and breakpoint manipulation
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel/>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: =?UTF-8?Q?Alex_Benn=c3=a9e?= <alex.bennee@linaro.org>, Paolo Bonzini <pbonzini@redhat.com>
Cc: mttcg@greensocs.com, qemu-devel@nongnu.org, fred konrad <fred.konrad@greensocs.com>, a rigo <a.rigo@virtualopensystems.com>, cota@braap.org, bobby prani <bobby.prani@gmail.com>, mark burton <mark.burton@greensocs.com>, jan kiszka <jan.kiszka@siemens.com>, rth@twiddle.net, peter maydell <peter.maydell@linaro.org>, claudio fontana <claudio.fontana@huawei.com>

On 20/06/16 19:27, Alex Bennée wrote:
> The watchpoint contention is the biggest one. FWIW I like the RCU
> approach because it is low impact when running (and I'm hoping faster as
> well by not being a linked list).

When can we expect any contention? I generally find the idea of RCU
really great, but in this particular case, I'm afraid, it could give us
less profit (performance) than pain (complexity).

> It's not a major problem in system mode because generally the system is
> halted when changes are made to the list. However I'd like to solve it
> properly for both system and user-mode so I can then forgot about
> another special case.

Could you please explain a bit more about problems in user-mode?

Thanks,
Sergey