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From: Alex =?utf-8?Q?Benn=C3=A9e?= <alex.bennee@linaro.org>
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Date: Tue, 12 Apr 2016 15:23:15 +0100
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Subject: Re: [Qemu-devel] [RFC v2 08/11] tcg: add options for enabling MTTCG
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To: Pavel Dovgalyuk <dovgaluk@ispras.ru>
Cc: 'Sergey Fedorov' <serge.fdrv@gmail.com>, 'KONRAD Frederic' <fred.konrad@greensocs.com>, 'Peter Maydell' <peter.maydell@linaro.org>, 'MTTCG Devel' <mttcg@listserver.greensocs.com>, 'Alvise Rigo' <a.rigo@virtualopensystems.com>, "'Emilio G. Cota'" <cota@braap.org>, 'QEMU Developers' <qemu-devel@nongnu.org>, 'Mark Burton' <mark.burton@greensocs.com>, 'Paolo Bonzini' <pbonzini@redhat.com>, "'J.
	Kiszka'" <jan.kiszka@siemens.com>, 'Richard Henderson' <rth@twiddle.net>, 'Claudio Fontana' <claudio.fontana@huawei.com>, 'Peter Crosthwaite' <crosthwaite.peter@gmail.com>, 'Andreas =?utf-8?Q?F=C3=A4rber'?= <afaerber@suse.de>


Pavel Dovgalyuk <dovgaluk@ispras.ru> writes:

>> From: mttcg-request@listserver.greensocs.com [mailto:mttcg-request@listserver.greensocs.com]
>> On 12/04/16 15:50, KONRAD Frederic wrote:
>> >> Yes, but users may like to have an option to disable MTTCG for some
>> >> reason. I'm also concerned about icount mode: not sure how to account
>> >> virtual time when all vCPUs run in parallel.
>> >
>> > I'm thinking the same, we don't have a solution for icount yet.
>> > The reverse execution support is probably badly broken as well.
>>
>> Reverse execution doesn't even seem to support more than a single core.
>> As of icount, it looks like to be incompatible with MTTCG.
>
> It doesn't, because there is no multicore support for tcg yet.
> I think, that we have to find some solution for icount (even if it
> will be slow).

Well one of the reasons I'm keeping single thread behaviour is so things
like icount/replay support can continue to work. The two options will be
incompatible to start with.

I'm also expecting people will want to rule out mttcg as a problem at
least in the early days.

--
Alex Bennée