Re: [PATCH 2/5] KVM: Implement CR read caching for KVM paravirt_ops

Avi Kivity wrote:

Anthony Liguori wrote:

quoted

+/*
+ * Control register reads can be trapped.  Since trapping is relatively
+ * expensive, we can avoid paying the cost by caching logically.
+ */
+static unsigned long kvm_read_cr(int reg)
+{
+    struct kvm_paravirt_state *state
+        = per_cpu(paravirt_state, smp_processor_id());
+
+    if (unlikely(!state->cr_valid[reg])) {
+        if (reg == 0)
+            state->cached_cr[reg] = native_read_cr0();
+        else if (reg == 3)
+            state->cached_cr[reg] = native_read_cr3();
+        else if (reg == 4)
+            state->cached_cr[reg] = native_read_cr4();
+        else
+            BUG();
+        state->cr_valid[reg] = 1;
+    }
+    return state->cached_cr[reg];
+}
+

It would be good to declare this (and kvm_write_cr) always_inline.  
These functions are never called with a non-constant reg parameters, 
and the unsightly if tree (more readable as a switch, IMO) will fold 
nicely when inlined.

Ok.

Regards,

Anthony Liguori



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