[RFC PATCH] powerpc/ftrace: Refactoring and support for -fpatchable-function-entry
Naveen N Rao
naveen at kernel.org
Sun May 21 04:17:22 AEST 2023
Christophe Leroy wrote:
>
>
> Le 20/05/2023 à 12:34, Christophe Leroy a écrit :
>>
>>
>> Le 19/05/2023 à 21:26, Naveen N Rao a écrit :
>>> [Vous ne recevez pas souvent de courriers de naveen at kernel.org.
>>> Découvrez pourquoi ceci est important à
>>> https://aka.ms/LearnAboutSenderIdentification ]
>>>
>>> Refactor ftrace code and move to using ftrace_replace_code() to help
>>> simplify and make the code more maintainable.
>>>
>>> - The existing ftrace.c code is moved to a separate file so that ppc64
>>> elfv1 and clang -pg only support continue. This makes it possible to
>>> converge ppc32 and ppc64 support further.
>>> - Drop code to re-purpose compiler-generated long branches for ftrace
>>> use in support of large kernels. We still retain the ftrace stubs at
>>> the end of .text, so we now support kernels upto ~64MB.
>>> - Add ftrace_init_nop() to keep boot-time validations and init separate
>>> from runtime.
>>> - Implement ftrace_replace_code() to simplify overall ftrace setup. This
>>> will be especially useful when adding ability to nop out 'mflr r0'
>>> later, and for other subsequent ftrace features.
>>> - Add support for -fpatchable-function-entry. On ppc64, this needs gcc
>>> v13.1 so that the nops are generated at LEP. This also moves ppc32 to
>>> using the same two-instruction sequence as that of ppc64.
>>>
>>> This applies atop patches 1-3 of Nick's series for elfv2 conversion, as
>>> well as Nick's patch enabling -mprofile-kernel for elfv2 BE:
>>> - https://lore.kernel.org/all/20230505071850.228734-1-npiggin@gmail.com/
>>> - https://lore.kernel.org/all/20230506011814.8766-1-npiggin@gmail.com/
>>>
>>> This builds for me and passes a quick test, posting this as an early
>>> RFC.
>>>
>>> Signed-off-by: Naveen N Rao <naveen at kernel.org>
>>
>> Looks good, works on PPC32 but I observed some performance degradation,
>> around 25% more time needed to activate function tracer and around 10%
>> more time needed to de-activate function tracer (by writting
>> function/nop into /sys/kernel/debug/tracing/current_tracer.
Thanks for the test!
I hadn't looked at the performance, though I was expecting it to be
better. On ppc64, I am actually not seeing much of a difference.
>
>
> perf record with your patch applied:
>
> 20.59% echo [kernel.kallsyms] [k] ftrace_check_record
> 15.71% echo [kernel.kallsyms] [k] patch_instruction
> 6.75% echo [kernel.kallsyms] [k] ftrace_replace_code
> 4.30% echo [kernel.kallsyms] [k] __ftrace_hash_rec_update
> 3.96% echo [kernel.kallsyms] [k]
> __rb_reserve_next.constprop.0
> 3.20% echo [kernel.kallsyms] [k] ftrace_get_call_inst.isra.0
> 2.62% echo [kernel.kallsyms] [k] ftrace_get_addr_new
> 2.44% echo [kernel.kallsyms] [k] ftrace_rec_iter_next
> 2.15% echo [kernel.kallsyms] [k] function_trace_call
> 2.09% echo [kernel.kallsyms] [k] rb_commit
> 1.92% echo [kernel.kallsyms] [k] ring_buffer_unlock_commit
> 1.69% echo [kernel.kallsyms] [k] ring_buffer_lock_reserve
> 1.63% echo [kernel.kallsyms] [k] copy_page
> 1.45% echo [kernel.kallsyms] [k]
> ftrace_create_branch_inst.constprop.0
> 1.40% echo [kernel.kallsyms] [k] unmap_page_range
> 1.34% echo [kernel.kallsyms] [k] mas_next_entry
> 1.28% echo ld-2.23.so [.] do_lookup_x
> 1.22% echo [kernel.kallsyms] [k] ftrace_call
> 1.05% echo [kernel.kallsyms] [k] trace_function
> 0.99% echo [kernel.kallsyms] [k] ftrace_caller
> 0.81% echo [kernel.kallsyms] [k] ftrace_rec_iter_record
>
> perf record without your patch:
>
> 22.58% echo [kernel.kallsyms] [k] patch_instruction
> 17.85% echo [kernel.kallsyms] [k] ftrace_check_record
> 11.65% echo [kernel.kallsyms] [k] ftrace_replace_code
> 6.76% echo [kernel.kallsyms] [k] ftrace_make_call
> 6.68% echo [kernel.kallsyms] [k] __ftrace_hash_rec_update
> 3.50% echo [kernel.kallsyms] [k] ftrace_get_addr_curr
> 3.42% echo [kernel.kallsyms] [k] ftrace_get_addr_new
> 2.36% echo [kernel.kallsyms] [k] copy_page
> 1.22% echo [kernel.kallsyms] [k] __rb_reserve_next.constprop.0
> 1.22% echo ld-2.23.so [.] do_lookup_x
> 1.06% echo [kernel.kallsyms] [k] ftrace_lookup_ip
> 0.73% echo ld-2.23.so [.] _dl_relocate_object
> 0.65% echo [kernel.kallsyms] [k] flush_dcache_icache_page
> 0.65% echo [kernel.kallsyms] [k] function_trace_call
That suggests ftrace_test_record() as the likely cause. The below change
does improve performance on ppc64. Can you see if it makes a difference
on ppc32?
Upstream/before the below change (ftrace activation):
0.15266 +- 0.00215 seconds time elapsed ( +- 1.41% )
With the below change:
0.14170 +- 0.00396 seconds time elapsed ( +- 2.79% )
- Naveen
---
diff --git a/arch/powerpc/kernel/trace/ftrace.c b/arch/powerpc/kernel/trace/ftrace.c
index a9d57f338bd78e..8b2096ec77bba2 100644
--- a/arch/powerpc/kernel/trace/ftrace.c
+++ b/arch/powerpc/kernel/trace/ftrace.c
@@ -167,23 +167,22 @@ void ftrace_replace_code(int enable)
for_ftrace_rec_iter(iter) {
rec = ftrace_rec_iter_record(iter);
- update = ftrace_test_record(rec, enable);
ip = rec->ip;
- new_addr = 0;
+ addr = ftrace_get_addr_curr(rec);
+ new_addr = ftrace_get_addr_new(rec);
+ update = ftrace_update_record(rec, enable);
switch (update) {
case FTRACE_UPDATE_IGNORE:
default:
continue;
case FTRACE_UPDATE_MODIFY_CALL:
- addr = ftrace_get_addr_curr(rec);
- new_addr = ftrace_get_addr_new(rec);
break;
case FTRACE_UPDATE_MAKE_CALL:
- addr = ftrace_get_addr_new(rec);
- break;
+ addr = new_addr;
+ fallthrough;
case FTRACE_UPDATE_MAKE_NOP:
- addr = ftrace_get_addr_curr(rec);
+ new_addr = 0;
break;
}
nop_inst = ppc_inst(PPC_RAW_NOP());
@@ -213,7 +212,6 @@ void ftrace_replace_code(int enable)
ret = ftrace_modify_code(ip, old, new);
if (ret)
goto out;
- ftrace_update_record(rec, enable);
}
out:
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