Re: [Xen-devel] schedule() vs softirqs

[Keir Fraser <keir@xxxxxxxxxxxxx>]

On 15/12/06 20:41, "Hollis Blanchard" <hollisb@xxxxxxxxxx> wrote:

> It's an issue with any architecture with a large number of registers
> which aren't automatically saved by hardware (and a C ABI that makes
> some of them non-volatile).
> 
> x86 has a small number of registers. ia64 automatically saves them (from
> what I understand). So of the currently-supported architectures, yes,
> that leaves PowerPC.

I see. It sounds like returning from context_switch() is perhaps the right
thing for powerpc. That would be easier if you have per-cpu stacks (like
ia64). If not there are issues in saving register state later (and hence
delaying your call to context_saved()) as there are calls to do_softirq()
outside your asm code (well, not many, but there is one in domain.c for
example) where you won't end up executing your do_softirq() wrapper. In
general we'd like to reserve the right to include voluntary yield points,
and that won't mix well with lazy register saves and per-physical-cpu
stacks.

 -- Keir


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