Le 20/05/2023 à 20:17, Naveen N Rao a écrit :

Christophe Leroy wrote:

quoted

Le 20/05/2023 à 12:34, Christophe Leroy a écrit :

quoted

Le 19/05/2023 à 21:26, Naveen N Rao a écrit :

quoted

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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/ (local)
- https://lore.kernel.org/all/20230506011814.8766-1-npiggin@gmail.com/ (local)

This builds for me and passes a quick test, posting this as an early
RFC.

Signed-off-by: Naveen N Rao <naveen@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.

quoted

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% )

That's better, but still more time than original implementation:

+20% to activate function tracer (was +40% with your RFC)
+21% to activate nop tracer (was +24% with your RFC)

perf record (without strict kernel rwx) :

     17.75%  echo     [kernel.kallsyms]   [k] ftrace_check_record
      9.76%  echo     [kernel.kallsyms]   [k] ftrace_replace_code
      6.53%  echo     [kernel.kallsyms]   [k] patch_instruction
      5.21%  echo     [kernel.kallsyms]   [k] __ftrace_hash_rec_update
      4.26%  echo     [kernel.kallsyms]   [k] ftrace_get_addr_curr
      4.18%  echo     [kernel.kallsyms]   [k] ftrace_get_call_inst.isra.0
      3.45%  echo     [kernel.kallsyms]   [k] ftrace_get_addr_new
      3.08%  echo     [kernel.kallsyms]   [k] function_trace_call
      2.20%  echo     [kernel.kallsyms]   [k] __rb_reserve_next.constprop.0
      2.05%  echo     [kernel.kallsyms]   [k] copy_page
      1.91%  echo     [kernel.kallsyms]   [k] 
ftrace_create_branch_inst.constprop.0
      1.83%  echo     [kernel.kallsyms]   [k] ftrace_rec_iter_next
      1.83%  echo     [kernel.kallsyms]   [k] rb_commit
      1.69%  echo     [kernel.kallsyms]   [k] ring_buffer_lock_reserve
      1.54%  echo     [kernel.kallsyms]   [k] trace_function
      1.39%  echo     [kernel.kallsyms]   [k] __call_rcu_common.constprop.0
      1.25%  echo     ld-2.23.so          [.] do_lookup_x
      1.17%  echo     [kernel.kallsyms]   [k] ftrace_rec_iter_record
      1.03%  echo     [kernel.kallsyms]   [k] unmap_page_range
      0.95%  echo     [kernel.kallsyms]   [k] flush_dcache_icache_page
      0.95%  echo     [kernel.kallsyms]   [k] ftrace_lookup_ip


Christophe