Re: [Qemu-devel] [RFC v4 5/9] configure: Enable/disable new qemu_{ld, st} excl insns

["Alex Bennée" <alex.bennee@linaro.org>]

Aurelien Jarno <aurelien@aurel32.net> writes:

> On 2015-08-09 09:11, Alex Bennée wrote:
>> 
>> Aurelien Jarno <aurelien@aurel32.net> writes:
>> 
>> > On 2015-08-07 19:03, Alvise Rigo wrote:
>> >> Introduce the new --enable-tcg-ldst-excl configure option to enable the
>> >> LL/SC operations only for those backends that support them.
>> >> 
>> >> Suggested-by: Jani Kokkonen <jani.kokkonen@huawei.com>
>> >> Suggested-by: Claudio Fontana <claudio.fontana@huawei.com>
>> >> Signed-off-by: Alvise Rigo <a.rigo@virtualopensystems.com>
>> >> ---
>> >>  configure | 21 +++++++++++++++++++++
>> >>  1 file changed, 21 insertions(+)
>> >
>> > We have seen that for this kind of patch, it's better to add support in
>> > all backends, otherwise it takes ages to get all the backends converted.
>> > I think you should involve the backend maintainers. I can try to provide
>> > the corresponding patches for mips and ia64.
>> 
>> We discussed this on the last MTTCG call and agree. However we will need
>> help from the other TCG maintainers for the backends. The changes should
>> be fairly mechanical though.
>> 
>> However in the spirit of keeping trees building in the meantime should
>> we change this from a configure option to just a static option for each
>> given backend as it is converted?
>
> I am not even sure we need a static option. I guess providing we are
> doing that early enough in the 2.5 cycle, we can just add the new ops
> and start using them. Of course we should put the backends maintainers
> in the loop so they can fix that quickly and don't get a surprise weeks
> afters.
>
> That said, please see my other email, I am not sure we actually need to
> modify backends, I think we can implement these new "ops" through
> tcg-runtime.

We still need to ensure "normal" ld/st operations trip the exclusive bit
though.

>
> Aurelien

-- 
Alex Bennée