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Date: Wed, 10 Nov 2010 10:29:45 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Hitoshi Mitake <mitake@dcl.info.waseda.ac.jp>
Cc: linux-kernel@vger.kernel.org, h.mitake@gmail.com,
        Ma Ling <ling.ma@intel.com>, Zhao Yakui <yakui.zhao@intel.com>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Arnaldo Carvalho de Melo <acme@redhat.com>,
        Paul Mackerras <paulus@samba.org>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Thomas Gleixner <tglx@linutronix.de>, "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH] perf bench: add --prefault option for causing page
 faults before benchmark
Message-ID: <20101110092945.GD12238@elte.hu>
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* Hitoshi Mitake <mitake@dcl.info.waseda.ac.jp> wrote:

> This patch adds --prefault option to perf bench mem memcpy.
> If user specify this option to perf bench mem memcpy, overhead of
> page faults will be removed from the score of memcpy().
> 
> Example of usage:
> | % ./perf bench mem memcpy -l 500MB
> | # Running mem/memcpy benchmark...
> | # Copying 500MB Bytes from 0x7fc036749010 to 0x7fc055b4a010 ...
> |
> |      628.526821 MB/Sec
> | mitake@X201i:~/linux/.../tools/perf% ./perf bench mem memcpy -l 500MB --prefault
> | # Running mem/memcpy benchmark...
> | # Copying 500MB Bytes from 0x7ff1b45e2010 to 0x7ff1d39e3010 ...
> |
> |        4.849256 GB/Sec

Ok, looks rather useful.

We are rather close to being able to apply these bits. We need a resolution for the 
arch/x86/lib/memcpy_64.S details. The ugliest are these kinds of #ifdefs:

+#ifndef PERF_BENCH
 .Lmemcpy_e:
        .previous
+#endif

What happens if we keep that label in place?

This:

+#ifndef PERF_BENCH
 ENTRY(__memcpy)
 ENTRY(memcpy)
        CFI_STARTPROC
+#else
+	.globl  memcpy_x86_64_unrolled
+memcpy_x86_64_unrolled:
+#endif

Could be removed if you defined an ENTRY() macro in perf, right?

This:

+#ifndef PERF_BENCH
+
        CFI_ENDPROC
 ENDPROC(memcpy)
 ENDPROC(__memcpy)

Could be solved by defining ENDPROC()/etc. macros in perf, right?

We could remove this #ifdef:

+#ifndef PERF_BENCH
+
 #include <linux/linkage.h>

 #include <asm/cpufeature.h>
 #include <asm/dwarf2.h>

+#endif /* PERF_BENCH */

if you added empty linkage.h, cpufeature.h and dwarf2.h files as 
tools/perf/util/include/linux/linkage.h, tools/perf/util/include/asm/cpufeature.h.

That linkage.h file could even contain a short perf version of the ENTRY() macro, 
etc.

That way we can avoid having to touch arch/x86/lib/memcpy_64.S altogether.

Thanks,

	Ingo