Date: Sun, 03 Jun 2012 10:19:01 +0300 From: Andriy Gapon <avg@FreeBSD.org> To: Attilio Rao <attilio@FreeBSD.org>, Mitsuru IWASAKI <iwasaki@jp.freebsd.org> Cc: freebsd-acpi@FreeBSD.org, freebsd-arch@FreeBSD.org Subject: cpu stopping [Was: preparation for x86/acpica/acpi_wakeup.c] Message-ID: <4FCB0FE5.4050607@FreeBSD.org> In-Reply-To: <CAJ-FndAfm4_XqFSwBqXK=cgWkE6YVrtkS5BbcH7zcRd-100xTw@mail.gmail.com> References: <20120603.002554.119853142.iwasaki@jp.FreeBSD.org> <CAJ-FndAfm4_XqFSwBqXK=cgWkE6YVrtkS5BbcH7zcRd-100xTw@mail.gmail.com>
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on 03/06/2012 00:39 Attilio Rao said the following: > The first thing to consider is that right now we only have 2 states > for CPUs: started and stopped. These states are controlled by > started_cpus and stopped_cpus masks respectively. It seems you really > want to add an intermediate level among the 2 where you have: started > -> suspended -> started -> suspended ... -> stopped and you need to > expand the mechanism for dealing with started and stopped cpus to do > that. I'm pretty sure this will be very helpful also for other > architectures that want to do the same. As the first thing I must admit that I haven't looked at the patch :-) But really I don't see why we need to differentiate between stopped and suspended state as both of them ultimately mean exactly the same thing - CPUs are spinning on some condition (and they are in a well-defined place and state). My view of how this should work is: - there can be only one master CPU that controls all other (slave) CPUs - the master sets entry and exit hooks - the master signals slaves to enter the stop state - the slaves execute the enter hook and start spinning on the release condition - the master does whatever it wants to do in this special system state - the master signals the slaves to resume - the slave exit the spin loop and execute the exit hook We have almost all of this in place. Only now we have different IPIs and different IPI handlers to do the job (cpustop_handler and cpususpend_handler). I think that the hooks model should be more universal. In my opinion, what really would deserve a completely independent path is the hard-stop case. As this can be invoked nested to the other cases. E.g. exotic situations like a breakpoint or a trap or a panic in the suspend or the normal stop code paths. -- Andriy Gapon
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