[RFC PATCH] powerpc/ftrace: Refactoring and support for -fpatchable-function-entry
Christophe Leroy
christophe.leroy at csgroup.eu
Sun May 21 03:48:56 AEST 2023
Le 20/05/2023 à 18:28, Christophe Leroy a écrit :
>
>
> 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.
>
>
> 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
It is even worse without CONFIG_STRICT_KERNEL_RWX:
With your patch, 41% more is spent when activating function tracer, and
24% more is spent when activating nop tracer.
With your patch (without strict kernel rwx):
22.95% echo [kernel.kallsyms] [k] ftrace_check_record
9.28% echo [kernel.kallsyms] [k] ftrace_replace_code
4.96% echo [kernel.kallsyms] [k] __ftrace_hash_rec_update
4.71% echo [kernel.kallsyms] [k] patch_instruction
4.26% echo [kernel.kallsyms] [k] function_trace_call
4.13% echo ld-2.23.so [.] do_lookup_x
3.68% echo [kernel.kallsyms] [k] unmap_page_range
3.29% echo [kernel.kallsyms] [k] ftrace_get_call_inst.isra.0
3.03% echo [kernel.kallsyms] [k] __softirqentry_text_start
2.58% echo [kernel.kallsyms] [k] ftrace_get_addr_new
2.00% echo [kernel.kallsyms] [k] copy_page
1.93% echo [kernel.kallsyms] [k] ring_buffer_lock_reserve
1.81% echo [kernel.kallsyms] [k] __rb_reserve_next.constprop.0
1.74% echo [kernel.kallsyms] [k] trace_function
1.16% echo [kernel.kallsyms] [k] ftrace_call
1.16% echo [kernel.kallsyms] [k] ftrace_rec_iter_next
1.03% echo [kernel.kallsyms] [k] mas_next_entry
0.97% echo [kernel.kallsyms] [k] tracing_gen_ctx_irq_test
0.90% echo [kernel.kallsyms] [k]
ftrace_create_branch_inst.constprop.0
0.90% echo [kernel.kallsyms] [k] ftrace_rec_iter_record
Without your patch:
14.35% echo [kernel.kallsyms] [k] ftrace_check_record
7.84% echo [kernel.kallsyms] [k] ftrace_replace_code
7.31% echo [kernel.kallsyms] [k] ring_buffer_lock_reserve
5.65% echo [kernel.kallsyms] [k] __ftrace_hash_rec_update
5.45% echo [kernel.kallsyms] [k] function_trace_call
5.05% echo [kernel.kallsyms] [k] patch_instruction
4.85% echo [kernel.kallsyms] [k] ftrace_make_call
3.65% echo [kernel.kallsyms] [k] trace_function
2.86% echo [kernel.kallsyms] [k] ftrace_get_addr_new
2.39% echo [kernel.kallsyms] [k] __rb_reserve_next.constprop.0
2.26% echo [kernel.kallsyms] [k] release_pages
2.19% echo [kernel.kallsyms] [k] ftrace_get_addr_curr
1.93% echo [kernel.kallsyms] [k] mas_next_entry
1.93% echo [kernel.kallsyms] [k] ring_buffer_unlock_commit
1.86% echo [kernel.kallsyms] [k] copy_page
1.66% echo [kernel.kallsyms] [k] unmap_page_range
1.59% echo [kernel.kallsyms] [k] ftrace_caller
1.40% echo [kernel.kallsyms] [k] __softirqentry_text_start
1.20% echo ld-2.23.so [.] do_lookup_x
1.06% echo [kernel.kallsyms] [k] page_remove_rmap
1.06% echo [kernel.kallsyms] [k] tracing_gen_ctx_irq_test
0.93% echo [kernel.kallsyms] [k] ftrace_lookup_ip
Christophe
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