PERFMON isn't operational on amd64

[John Baldwin]

On Tuesday, July 27, 2010 3:06:50 pm Bruce Evans wrote:
> On Tue, 27 Jul 2010, John Baldwin wrote:
> 
> > On Tuesday, July 27, 2010 8:43:00 am pluknet wrote:
> >> Hi.
> >>
> >> What is a status of "options PERFMON" on amd64?
> >> ...
> >> Looking at cvs I see amd64/include/perfmon.h was never here.
> >
> > PERFMON in general is obsoleted by hwpmc(4) which is far more useful and
> > featureful.  It should probably just be axed.
> 
> Nothing should just be axed.
> 
> hwpmc(4) is far too featureful for me, yet perfmon(4) still does things
> for me that hwpmc cannot do:
> - from userland, without using the library, try undocumented unnamed
>    counters.  There are a few useful ones for k7.  E.g.:
>      0xc8 (k8-fr-retired-near-returns) and
>      0xc9 (k8-fr-retired-near-returns-mispredicted)
>    are k8-only according to hwpmc and amd docs, but also work on my k7
>    (after a 4-line fix for perfmon on kx).

I believe this is not too terribly hard to fix.  For the two above I think 
this will suffice (manpage would also need to be updated for a full patch):

(I think the misordering in pmc_events.h is required to preserve userland 
ABI.)

Index: hwpmc_amd.c
===================================================================
--- hwpmc_amd.c	(revision 210547)
+++ hwpmc_amd.c	(working copy)
@@ -137,6 +137,8 @@
 	{ PMC_EV_K7_RETIRED_TAKEN_BRANCHES_MISPREDICTED, 0xC5, 0 },
 	{ PMC_EV_K7_RETIRED_FAR_CONTROL_TRANSFERS, 0xC6, 0 },
 	{ PMC_EV_K7_RETIRED_RESYNC_BRANCHES,	0xC7, 0 },
+	{ PMC_EV_K7_RETIRED_NEAR_RETURNS,	0xC8, 0 },
+	{ PMC_EV_K7_RETIRED_NEAR_RETURNS_MISPREDICTED, 0xC9, 0 },
 	{ PMC_EV_K7_INTERRUPTS_MASKED_CYCLES,	0xCD, 0 },
 	{ PMC_EV_K7_INTERRUPTS_MASKED_WHILE_PENDING_CYCLES, 0xCE, 0 },
 	{ PMC_EV_K7_HARDWARE_INTERRUPTS,	0xCF, 0 },
Index: pmc_events.h
===================================================================
--- pmc_events.h	(revision 210547)
+++ pmc_events.h	(working copy)
@@ -74,10 +74,12 @@
 __PMC_EV(K7, RETIRED_RESYNC_BRANCHES)			\
 __PMC_EV(K7, INTERRUPTS_MASKED_CYCLES)			\
 __PMC_EV(K7, INTERRUPTS_MASKED_WHILE_PENDING_CYCLES)	\
-__PMC_EV(K7, HARDWARE_INTERRUPTS)
+__PMC_EV(K7, HARDWARE_INTERRUPTS)			\
+__PMC_EV(K7, RETIRED_NEAR_RETURNS)			\
+__PMC_EV(K7, RETIRED_NEAR_RETURNS_MISPREDICTED)
 
 #define	PMC_EV_K7_FIRST	PMC_EV_K7_DC_ACCESSES
-#define	PMC_EV_K7_LAST	PMC_EV_K7_HARDWARE_INTERRUPTS
+#define	PMC_EV_K7_LAST	PMC_EV_K7_RETIRED_NEAR_RETURNS_MISPREDICTED
 
 
 /*

> - in the kernel count, events at the level of individual functions, non-
>    statistically using high resolution kernel profiling.  This may result
>    in more time spent counting than doing useful work, but provides
>    high resolution.

I would rather us provide this via hwpmc(4).  perfmon(4) does not support
programmable events on modern Intel CPUs nor does it support non-x86 CPUs.

-- 
John Baldwin