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From: Sergey Fedorov <serge.fdrv@gmail.com>
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Date: Tue, 12 Apr 2016 15:42:01 +0300
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Subject: Re: [Qemu-devel] [RFC v2 08/11] tcg: add options for enabling MTTCG
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To: Peter Maydell <peter.maydell@linaro.org>, =?UTF-8?Q?Alex_Benn=c3=a9e?= <alex.bennee@linaro.org>
Cc: MTTCG Devel <mttcg@listserver.greensocs.com>, =?UTF-8?B?S09OUkFEIEZyw6lkw6lyaWM=?= <fred.konrad@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>, =?UTF-8?Q?Andreas_F=c3=a4rber?= <afaerber@suse.de>

On 12/04/16 14:59, Peter Maydell wrote:
> On 12 April 2016 at 12:48, Alex Bennée <alex.bennee@linaro.org> wrote:
>> Sergey Fedorov <serge.fdrv@gmail.com> writes:
>>> Maybe we'd better use existing qemu accelerator framework and introduce
>>> "-machine accel=mttcg" option?
>> My worry would be breaking existing code which assumes kvm | tcg. We
>> will want to enable mttcg by default for combos that work without having
>> to tweak tooling that already uses the -machine options.
> Comments from the peanut gallery:
>  * We definitely want to just default to MTTCG where it works:
> users shouldn't have to add new command line switches to get the
> better performance etc, because in practice that won't happen
>  * Anything that adds a new command line option at all has to
> be supported practically forever, so options that are only
> useful for a transitional period are worth thinking twice about

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.

Kind regards,
Sergey