[PATCH V2 1/2] Documentation/features: Add na key to arch-support.txt

[PATCH V2 1/2] Documentation/features: Add na key to arch-support.txt

[Ananth N Mavinakayanahalli]

To be used for features we will not support on a particular architecture.
The git log that adds this needs to provide the justification 'why?'

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

diff --git a/Documentation/features/arch-support.txt b/Documentation/features/arch-support.txt
index d22a109..f2b272e 100644
--- a/Documentation/features/arch-support.txt
+++ b/Documentation/features/arch-support.txt
@@ -8,4 +8,5 @@ The meaning of entries in the tables is:
     | ok |  # feature supported by the architecture
     |TODO|  # feature not yet supported by the architecture
     | .. |  # feature cannot be supported by the hardware
+    | na |  # feature will not be supported by the architecture
 

[PATCH V2 2/2] kprobes: Mark OPTPROBES na for powerpc

[Ananth N Mavinakayanahalli]

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 (one 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.

Hence, mark OPTPROBES na for powerpc.

Signed-off-by: Ananth N Mavinakayanahalli <ananth@in.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 |

Re: [PATCH V2 1/2] Documentation/features: Add na key to arch-support.txt

[Masami Hiramatsu]

On 2015/07/17 19:51, Ananth N Mavinakayanahalli wrote:
> To be used for features we will not support on a particular architecture.
> The git log that adds this needs to provide the justification 'why?'
> 
> Signed-off-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
> ---
>  Documentation/features/arch-support.txt |    1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/Documentation/features/arch-support.txt b/Documentation/features/arch-support.txt
> index d22a109..f2b272e 100644
> --- a/Documentation/features/arch-support.txt
> +++ b/Documentation/features/arch-support.txt
> @@ -8,4 +8,5 @@ The meaning of entries in the tables is:
>      | ok |  # feature supported by the architecture
>      |TODO|  # feature not yet supported by the architecture
>      | .. |  # feature cannot be supported by the hardware
> +    | na |  # feature will not be supported by the architecture

"will not" sounds like someone's will. I guess it could be "feature is useless/needless
on the architecture".

Thank you,



-- 
Masami HIRAMATSU
Linux Technology Research Center, System Productivity Research Dept.
Center for Technology Innovation - Systems Engineering
Hitachi, Ltd., Research & Development Group
E-mail: masami.hiramatsu.pt@hitachi.com