Hollis Blanchard wrote:
On Mon, 2008-07-07 at 15:56 +0200, ehrhardt@xxxxxxxxxxxxxxxxxx wrote:
From: Christian Ehrhardt <ehrhardt@xxxxxxxxxxxxxxxxxx>
The current implementation of kvmtrace uses always a 64 bit cycle variable,
but get_cycles() which is used to fill it is "unsigned long" which might be 32
bit.
This reduces the accuracy e.g. on embedded powerpc since we would have a 64bit
value but get_cycle() only returns the low 32 bit.
To solve that this patch introduces kvm_arch_trace_cycles() which allows us
to make this calculation architecture aware. That way every architecture can
insert whatever fits best for their "kvmtrace cycle counter".
Signed-off-by: Christian Ehrhardt <ehrhardt@xxxxxxxxxxxxxxxxxx>
Just one comment below...
BTW, because this breaks the ia64 and s390 builds, it might be nice to
CC the appropriate list/maintainer directly.
you're right - I'll add dummy stubs for ia64&s390 using the classic
get_cycle() call and resubmit the series.
---
[diffstat]
arch/powerpc/kvm/powerpc.c | 25 +++++++++++++++++++++++++
arch/x86/kvm/x86.c | 5 +++++
include/linux/kvm_host.h | 2 ++
virt/kvm/kvm_trace.c | 2 +-
4 files changed, 33 insertions(+), 1 deletion(-)
[diff]
diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
--- a/arch/powerpc/kvm/powerpc.c
+++ b/arch/powerpc/kvm/powerpc.c
@@ -521,6 +521,31 @@
return r;
}
+/*
+ * We need a 64 bit value here and the default get_cycles has only 32bit (tbl)
+ * on 32bit ppc. Since we have a 64bit counter for that we provide it here in
+ * full resolution for the trace records.
+*/
+__u64 kvm_arch_trace_cycles()
+{
+ unsigned long ruval;
+ unsigned long ruval2;
+ unsigned long rlval;
+
+ /* get a consistant pair of upper/lower timebase (no wrap occured) */
+ asm volatile(
+ "loop:\n"
+ "mftbu %0\n"
+ "mftbl %1\n"
+ "mftbu %2\n"
+ "cmpw %0, %2\n"
+ "bne loop"
+ : "=r" (ruval), "=r" (rlval), "=r" (ruval2)
+ );
+
+ return (((__u64)ruval) << 32) | rlval;
+}
You should use get_tb() here (see asm-powerpc/time.h).
yep does the same, I didn't see it and coded the asm from the processor
manual hint at the time base register.
Anyway - I'll change the code to get_tb() - thanks for the hint.
--
Grüsse / regards,
Christian Ehrhardt
IBM Linux Technology Center, Open Virtualization
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