(replying all because qemu-devel rejected my email again) On Thu, 16 Feb 2023 at 10:19, Alex Bennée <alex.ben...@linaro.org> wrote:
> Hi Juan, > > Do we have an agenda for next weeks KVM call yet? If there is space I'd > like to take some time to discuss the future direction of icount. > > Specifically I believe there might be some proposals for how we could > support icount with MTTCG worth discussing. From my point of view icount > provides too things: > > - a sense of time vaguely related to execution rather than wall clock > - determinism > > I would love to divorce the former from icount and punt it to plugins. > The plugin would be free to instrument as heavily or lightly as it sees > fit and provide its best guess as to guest time on demand. I wrote this > idea up as a card in Linaro's JIRA if anyone is interested: > > https://linaro.atlassian.net/browse/QEMU-481 > > Being able to punt cost modelling and sense of time into plugins would > allow the core icount support to concentrate on determinism. Then any > attempt to enable icount for MTTCG would then have to ensure it stays > deterministic. > > Richard and I have discussed the problem a few times and weren't sure it > was solvable but I'm totally open to hearing ideas on how to do it. > Fundamentally I think we would have to ensure any TB's doing IO would > have to execute in an exclusive context. The TCG code already has > mechanisms to ensure all IO is only done at the end of blocks so it > doesn't seem a huge leap to ensure we execute those blocks exclusively. > However there is still the problem of what to do about other pure > computation threads getting ahead or behind of the IO blocks on > subsequent runs. > > Anyway does anyone else have ideas to bring to the discussion? > > -- > Alex Bennée > Virtualisation Tech Lead @ Linaro > -- Alex Bennée Emulation and Virtualisation Tech Lead @ Linaro
