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Re: [Xen-devel] [PATCH 2/2] x86/HVM: Use fixed TSC value when saving or restoring domain

On 03/31/2014 10:34 AM, Jan Beulich wrote:

index 95b4b91..032eb23 100644
--- a/xen/include/xen/time.h
+++ b/xen/include/xen/time.h
@@ -32,7 +32,8 @@ struct vcpu;
   typedef s64 s_time_t;
   #define PRI_stime PRId64
-s_time_t get_s_time(void);
+s_time_t get_s_time_fixed(u64 at_tick);
+#define get_s_time() get_s_time_fixed(0)
get_s_time(), through NOW(), has quite many users, so I'm not certain
the code bloat resulting from this is desirable. I'd suggest the function
to remain such; the compiler will be able to make it a mov+jmp.
Sorry, not sure I understand what you are asking for.

There shouldn't be much of code size increase since get_s_time()
currently (and get_s_time_fixed() after this patch is applied) are not
inlines. The only increase is due to routine itself getting very
slightly larger.

But I suspect you meant something else.
All call sites have to zero %edi with the change in place, and I
was trying to tell you that the number of call sites of this isn't
exactly small due to the function's use via NOW(). Hence I think
you shouldn't penalize the callers and have an explicit out of line

OK, I understand the concern now but still confused about what you want ;-(

Two separate routines that only differ in how tsc is calculated (rdtscll vs. an 'in' parameter)?


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