linux-kernel - [PATCH V3 2/2] kprobes: Mark OPTPROBES na for powerpc

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Message-ID: <20150720105417.24801.66440.stgit@thinktux.in.ibm.com>
Date:	Mon, 20 Jul 2015 16:24:22 +0530
From:	Ananth N Mavinakayanahalli <ananth@...ibm.com>
To:	masami.hiramatsu.pt@...achi.com, mpe@...erman.id.au,
	mingo@...nel.org
Cc:	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: [PATCH V3 2/2] kprobes: Mark OPTPROBES na for powerpc

Kprobes uses a breakpoint instruction to trap into execution flow
and the probed instruction is single-stepped from an alternate location.

On some architectures like x86, under certain conditions, the OPTPROBES
feature enables replacing the probed instruction with a jump instead,
resulting in a significant perfomance boost (both the breakpoint and
single-step exception is bypassed for each kprobe).

Powerpc has an in-kernel instruction emulator. Kprobes on powerpc uses
this emulator already and bypasses the single-step exception, with a
lot less complexity. There is a potential gain to be had with a direct
jump instead of a breakpoint, but the caveats need to be traded off
with the complexity it brings in.

For now, mark OPTPROBES na for powerpc.

Signed-off-by: Ananth N Mavinakayanahalli <ananth@...ibm.com>
---
 .../features/debug/optprobes/arch-support.txt      |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Documentation/features/debug/optprobes/arch-support.txt b/Documentation/features/debug/optprobes/arch-support.txt
index b8999d8..73662f9 100644
--- a/Documentation/features/debug/optprobes/arch-support.txt
+++ b/Documentation/features/debug/optprobes/arch-support.txt
@@ -27,7 +27,7 @@
     |       nios2: | TODO |
     |    openrisc: | TODO |
     |      parisc: | TODO |
-    |     powerpc: | TODO |
+    |     powerpc: |  na  |
     |        s390: | TODO |
     |       score: | TODO |
     |          sh: | TODO |

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