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Re: [Xen-devel] [PATCH v4 14/17] x86/VPMU: Save VPMU state for PV guests during context switch

On 02/04/2014 06:38 AM, Jan Beulich wrote:
On 21.01.14 at 20:08, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx> wrote:
Save VPMU state during context switch for both HVM and PV guests unless we
are in PMU privileged mode (i.e. dom0 is doing all profiling) and the
out domain is not the control domain. The latter condition is needed because
me may have just turned the privileged PMU mode on and thus need to save
last domain.
While this is understandable, ...

--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -1444,17 +1444,16 @@ void context_switch(struct vcpu *prev, struct vcpu 
if (prev != next)
-        update_runstate_area(prev);
-    if ( is_hvm_vcpu(prev) )
-        if (prev != next)
+        update_runstate_area(prev);
+        if ( !(vpmu_mode & XENPMU_MODE_PRIV) ||
+             !is_control_domain(prev->domain) )
... I'd really like you to investigate ways to achieve the same effect
without this extra second condition added to the context switch path.
E.g. by synchronously issuing a save on all affected vCPU-s when
privileged mode gets turned on.

Yes, I should do something like that.


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