Re: [PATCH V3 2/2] kprobes: Mark OPTPROBES na for powerpc
On Mon, 2015-07-20 at 08:41 -0500, Segher Boessenkool wrote: > On Mon, Jul 20, 2015 at 04:24:22PM +0530, Ananth N Mavinakayanahalli wrote: > > 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. > > If we haven't yet investigated whether this feature is something beneficial > to the powerpc kernel, it should just stay as TODO, not be marked as n/a. Yep, agreed. As discussed in the other thread we'll leave this as TODO until we know it's either not a win or not worth the complexity. cheers -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH V3 2/2] kprobes: Mark OPTPROBES na for powerpc
On Mon, Jul 20, 2015 at 04:24:22PM +0530, Ananth N Mavinakayanahalli wrote: > 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. If we haven't yet investigated whether this feature is something beneficial to the powerpc kernel, it should just stay as TODO, not be marked as n/a. Segher -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
[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 --- .../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 | -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
[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 ana...@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 | -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH V3 2/2] kprobes: Mark OPTPROBES na for powerpc
On Mon, Jul 20, 2015 at 04:24:22PM +0530, Ananth N Mavinakayanahalli wrote: 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. If we haven't yet investigated whether this feature is something beneficial to the powerpc kernel, it should just stay as TODO, not be marked as n/a. Segher -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH V3 2/2] kprobes: Mark OPTPROBES na for powerpc
On Mon, 2015-07-20 at 08:41 -0500, Segher Boessenkool wrote: On Mon, Jul 20, 2015 at 04:24:22PM +0530, Ananth N Mavinakayanahalli wrote: 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. If we haven't yet investigated whether this feature is something beneficial to the powerpc kernel, it should just stay as TODO, not be marked as n/a. Yep, agreed. As discussed in the other thread we'll leave this as TODO until we know it's either not a win or not worth the complexity. cheers -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
