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[PATCH] arm64: ftrace: stop using kstop_machine to enable/disable tracing

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  [PATCH] arm64: ftrace: stop using kstop_machine to enable/disable tracing Li Bin <huawei.libin@huawei.com> - 2015-11-28 09:00 +0100
    Re: [PATCH] arm64: ftrace: stop using kstop_machine to  enable/disable tracing Steven Rostedt <rostedt@goodmis.org> - 2015-11-28 17:00 +0100
      Re: [PATCH] arm64: ftrace: stop using kstop_machine to enable/disable  tracing libin <huawei.libin@huawei.com> - 2015-11-30 03:10 +0100

#1279110 — [PATCH] arm64: ftrace: stop using kstop_machine to enable/disable tracing

On arm64, kstop_machine which is hugely disruptive to a running
system is not needed to convert nops to ftrace calls or back,
because that modifed code is a single 32bit instructions which
is impossible to cross cache (or page) boundaries, and the used str
instruction is single-copy atomic.

Cc: <stable@vger.kernel.org> # 3.18+
Signed-off-by: Li Bin <huawei.libin@huawei.com>
---
 arch/arm64/kernel/ftrace.c |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c
index c851be7..9669b33 100644
--- a/arch/arm64/kernel/ftrace.c
+++ b/arch/arm64/kernel/ftrace.c
@@ -93,6 +93,11 @@ int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
 	return ftrace_modify_code(pc, old, new, true);
 }
 
+void arch_ftrace_update_code(int command)
+{
+	ftrace_modify_all_code(command);
+}
+
 int __init ftrace_dyn_arch_init(void)
 {
 	return 0;
-- 
1.7.1

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#1279160 — Re: [PATCH] arm64: ftrace: stop using kstop_machine to enable/disable tracing

On Sat, 28 Nov 2015 15:50:09 +0800
Li Bin <huawei.libin@huawei.com> wrote:

> On arm64, kstop_machine which is hugely disruptive to a running
> system is not needed to convert nops to ftrace calls or back,
> because that modifed code is a single 32bit instructions which
> is impossible to cross cache (or page) boundaries, and the used str
> instruction is single-copy atomic.

Is this really true? I thought that arm (and then perhaps arm64) has
some 2 byte instructions. If that's the case it is very well possible
that a 4 byte instruction can cross cache lines.

-- Steve

> 
> Cc: <stable@vger.kernel.org> # 3.18+
> Signed-off-by: Li Bin <huawei.libin@huawei.com>
> ---
>  arch/arm64/kernel/ftrace.c |    5 +++++
>  1 files changed, 5 insertions(+), 0 deletions(-)
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#1279498 — Re: [PATCH] arm64: ftrace: stop using kstop_machine to enable/disable tracing

on 2015/11/28 23:58, Steven Rostedt wrote:
> On Sat, 28 Nov 2015 15:50:09 +0800
> Li Bin <huawei.libin@huawei.com> wrote:
>
>> On arm64, kstop_machine which is hugely disruptive to a running
>> system is not needed to convert nops to ftrace calls or back,
>> because that modifed code is a single 32bit instructions which
>> is impossible to cross cache (or page) boundaries, and the used str
>> instruction is single-copy atomic.
> Is this really true? I thought that arm (and then perhaps arm64) has
> some 2 byte instructions. If that's the case it is very well possible
> that a 4 byte instruction can cross cache lines.

When system in aarch32 state, it will use A32 or T32 instrucion set, and
T32 (thumb) have 16-bit instructions. But arm64 that in aarch64 state only
using A64 instruction set, which is a clean and fixed length instruction
set that instuctions are always 32 bits wide. Right?

Thanks,
Li Bin

> -- Steve
>
>> Cc: <stable@vger.kernel.org> # 3.18+
>> Signed-off-by: Li Bin <huawei.libin@huawei.com>
>> ---
>>  arch/arm64/kernel/ftrace.c |    5 +++++
>>  1 files changed, 5 insertions(+), 0 deletions(-)
> .
>


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