On Fri, Jun 15, 2018 at 12:00:20AM +0200, Greg Kurz wrote:
> On Thu, 14 Jun 2018 09:52:55 -1000
> Richard Henderson <richard.hender...@linaro.org> wrote:
>
> > On 06/12/2018 10:19 PM, Greg Kurz wrote:
> > > I'm confused... I don't see anything related to HTM in TCG. Also we have
> > > the following in cap_htm_apply():
> > >
> > > if (tcg_enabled()) {
> > > error_setg(errp,
> > > "No Transactional Memory support in TCG, try
> > > cap-htm=off");
> > >
> > > I'm probably missing something... can you enlighten me ?
> >
> > One of the two IBM machines -- and I thought it was ppc not s390x, but the
> > code
> > you quote seems to deny that memory -- has stub support for TM within TCG.
>
> Oh ? I didn't know and didn't check :)
That is true, there are stub implementations of the TM instructions.
>
> > To wit, the instructions are recognized and transactions always fail.
> > Which is
> > not a bad way to test the required fallback paths that rarely fail on
> > hardware.
> > ;-)
>
> If TM instructions don't cause an exception, I guess its reasonable to say
> they're supported :)
That argument has come up before, and I disagree. I don't think it's
reasonable to advertise TM support as available if the instructions
always fail.
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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