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Date: Fri, 15 Nov 2013 06:46:09 +0100
From: Ingo Molnar <mingo@...nel.org>
To: David Ahern <dsahern@...il.com>
Cc: acme@...stprotocols.net, linux-kernel@...r.kernel.org,
Frederic Weisbecker <fweisbec@...il.com>,
Jiri Olsa <jolsa@...hat.com>,
Namhyung Kim <namhyung@...nel.org>
Subject: Re: [PATCH] perf top: Make -g refer to callchains
btw., here's some 'perf top' call graph performance and profiling
quality feedback, with the latest perf code:
'perf top --call-graph fp' now works very well, using just 0.2%
of CPU time on a fast system:
4676 mingo 20 0 612m 56m 9948 S 1 0.2 0:00.68 perf
'perf top --call-graph dwarf' on the other hand is horrendously
slow, using 20% of CPU time on a 4 GHz CPU:
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
4646 mingo 20 0 658m 81m 12m R 19 0.3 0:18.17 perf
On another system with a 2.4GHz CPU it's taking up 100% of CPU
time (!):
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
8018 mingo 20 0 290320 45220 8520 R 99.5 0.3 0:58.81 perf
Profiling 'perf top' shows all sorts of very high dwarf
processing overhead:
#
# Overhead Command Shared Object Symbol
# ........ ....... ......................... .................................................
#
7.08% perf perf [.] access_mem
7.03% perf perf [.] dso__data_read_offset
5.83% perf perf [.] maps__find
5.64% perf libunwind-x86_64.so.8.0.1 [.] 0x000000000000ba25
4.75% perf perf [.] thread__find_addr_map
3.81% perf [kernel.kallsyms] [k] unmap_single_vma
2.57% perf perf [.] map__map_ip
2.48% perf libelf-0.156.so [.] 0x0000000000003a84
2.12% perf [kernel.kallsyms] [k] memset
2.12% perf perf [.] dso__data_read_addr
2.10% perf libc-2.17.so [.] __memcpy_sse2
1.72% perf libc-2.17.so [.] __memset_sse2
1.58% perf [kernel.kallsyms] [k] page_fault
1.56% perf libc-2.17.so [.] __memset_x86_64
1.44% perf perf [.] find_proc_info
1.25% perf libelf-0.156.so [.] elf_end
1.19% perf [kernel.kallsyms] [k] flush_tlb_mm_range
1.06% perf libc-2.17.so [.] vfprintf
1.04% perf libunwind-x86_64.so.8.0.1 [.] _Ux86_64_dwarf_search_unwind_table
1.00% perf [kernel.kallsyms] [k] __audit_syscall_exit
0.94% perf libc-2.17.so [.] _int_free
0.92% perf libc-2.17.so [.] _int_malloc
0.84% perf libc-2.17.so [.] __memcmp_sse2
0.81% perf [kernel.kallsyms] [k] unmapped_area_topdown
0.71% perf [kernel.kallsyms] [k] system_call
0.71% perf [kernel.kallsyms] [k] system_call_after_swapgs
0.65% perf [kernel.kallsyms] [k] sysret_check
0.63% perf perf [.] dso__find_symbol
0.58% perf [kernel.kallsyms] [k] clear_page_c
0.58% perf [kernel.kallsyms] [k] handle_mm_fault
0.56% perf libc-2.17.so [.] __sigprocmask
0.55% perf [kernel.kallsyms] [k] copy_user_generic_string
0.51% perf [kernel.kallsyms] [k] __do_fault
0.49% perf [kernel.kallsyms] [k] find_vma
0.47% perf libpthread-2.17.so [.] __libc_close
0.44% perf [kernel.kallsyms] [k] __audit_syscall_entry
0.44% perf [kernel.kallsyms] [k] mmap_region
0.42% perf [kernel.kallsyms] [k] _raw_spin_lock
0.41% perf [kernel.kallsyms] [k] kmem_cache_free
0.40% perf [kernel.kallsyms] [k] kmem_cache_alloc
0.40% perf libpthread-2.17.so [.] pthread_mutex_unlock
0.37% perf [kernel.kallsyms] [k] perf_event_aux_ctx
0.37% perf [kernel.kallsyms] [k] do_munmap
0.37% perf libc-2.17.so [.] free
[...]
Thanks,
Ingo
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