Re: [PATCH resend] Perf-tool/MIPS: support cross compiling of tools/perf for MIPS

[Deng-Cheng Zhu <dengcheng.zhu@gmail.com>]

Thanks guys. So let's turn the patch into the following?

Signed-off-by: Deng-Cheng Zhu<dengcheng.zhu@gmail.com>
---
  tools/perf/perf.h |   14 ++++++++++++++
  1 files changed, 14 insertions(+), 0 deletions(-)

diff --git a/tools/perf/perf.h b/tools/perf/perf.h
index 6fb379b..cd05284 100644
--- a/tools/perf/perf.h
+++ b/tools/perf/perf.h
@@ -73,6 +73,20 @@
  #define cpu_relax()	asm volatile("":::"memory")
  #endif

+#ifdef __mips__
+#include "../../arch/mips/include/asm/unistd.h"
+#define rmb()		asm volatile(					\
+				".set	push\n\t"			\
+				".set	noreorder\n\t"			\
+				".set	mips2\n\t"			\
+				"sync\n\t"				\
+				".set	pop"				\
+				: /* no output */			\
+				: /* no input */			\
+				: "memory")
+#define cpu_relax()	asm volatile("" ::: "memory")
+#endif
+
  #include<time.h>
  #include<unistd.h>
  #include<sys/types.h>


On 2010-10-2 9:59, Ralf Baechle wrote:
> On Fri, Oct 01, 2010 at 02:45:17PM -0700, David Daney wrote:
>
>> In user space the rmb() must expand to a SYNC instruction.  I am not
>> sure what your version in the patch is doing with all those NOPs.  That
>> is not guaranteed to do anything.
> That's a rather old version of the kernel rmb macro I think.  The NOPs
> where there to enforce ordering of a mix of cached and uncached accesses
> on the R4400 (not R4000) where according to my reading the manual leaves
> it a bit unclear if a SYNC is sufficient or if the pipeline needs to be
> drained in addition.  See version 2 of the R4000/R4400 User's Manual.
>
>> The instruction set specifications say that SYNC orders all loads and
>> stores.  This is a heaver operation than rmb() demands, but is the only
>> universally available instruction that imposes ordering.
>>
>> For processors that do not support SYNC, the kernel will emulate it, so
>> it is safe to use in userspace.  I wouldn't worry about emulation
>> overhead though, because processors that lack SYNC probably also lack
>> performance counters, so are not as interesting from a perf-tool point
>> of view.
> Yes, just use SYNC.  SYNC-less processors would only be R2000/R3000
> processors and a few other oddball processors which for performance
> optimization are totally uninteresting since years.
>
>    Ralf