Messages in this thread |  | | Date | Mon, 11 Sep 2006 09:55:05 +0200 | | From | Ingo Molnar <> | | Subject | Re: 2.6.18-rc6-mm1: GPF loop on early boot |
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* Jeremy Fitzhardinge <jeremy@goop.org> wrote:
> Ingo Molnar wrote: > >btw., what's the connection of %gs based PDA to Xen and > >paravirtualization in general - %esp based current is just as > >Xen-friendly, or am i wrong? I guess there must be some connection, > >given that you are working on this ;) > > > > Yep. The goal is to put the Xen VCPU structure into the PDA, so that it > can be easily accessed. At present, masking events (ie, cli), is > something along the lines of > > xen_shared_info->vcpu[smp_processor_id()].mask = 1 > > which comes out to something like 20 bytes of code, and is probably too > awkward to inline. If the vcpu is in the PDA, it would come out to: > > movb $1, %gs:xen_vcpu_mask > > which has the added benefit of not needing a register.
take a look at lockdep: amongst other things it adds the TRACE_IRQFLAGS / irqflags.h infrastructure, which could easily be modified to allow the easy replacement of cli/sti/pushf/popf. I wrote it with the side-goal of paravirtualization. I.e. instead of the DISABLE_INTERRUPT / ENABLE_INTERRUPT duplication you do in -mm currently please just enhance irqflags.h to cover the needs of paravirtualization too. (most of which should be the moving of cli/sti into the assembly callbacks)
into that the PDA would plug in a natural way: current->hardirqs_enabled is basically just an alias for !xen_shared_info->vcpu[smp_processor_id()].mask.
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