Re: [Qemu-devel] Re: [PATCH 0/7] KVM SMP support, early version

[Jan Kiszka <jan.kiszka@siemens.com>]

Glauber Costa wrote:
> On Mon, Nov 30, 2009 at 2:40 PM, Avi Kivity <avi@redhat.com> wrote:
>> On 11/30/2009 05:55 PM, Glauber Costa wrote:
>>> reset code is responsible for most remote calls in qemu. One of the
>>> only ones we still
>>> have left is the gdb stuff. Do you have any suggestion to do that
>>> without the current
>>> on_vcpu mechanism?
>>>
>> No.  But what's wrong with on_vcpu?
> 
> intrinsically racy. signal passing slow down things, etc.
> 
> That said, as I've stated many times: I don't believe there's anything
> fundamentally wrong with on_vcpu. But we might get benefits from a re-design
> of things to avoid it whenever possible. (just like the vcpu_reset()
> I've just posted)
> 

If you don't want immediate execution of update_guest_debug, save the
state that shall be transferred, set some flag, and run the transfer
before guest entry inside the vcpu threads (after putting the registers
as older kernels may otherwise overwrite the flags register). Should
work, may even avoid redundant calls during a gdb session.

Jan

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