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SubjectRe: [PATCH] perf: replace automatic const char[] variables by statics
Em Sat, Nov 03, 2018 at 12:06:23AM +0100, Rasmus Villemoes escreveu:
> An automatic const char[] variable gets initialized at runtime, just
> like any other automatic variable. For long strings, that uses a lot of
> stack and wastes time building the string; e.g. for the "No %s
> allocation events..." case one has
>
> 444516: 48 b8 4e 6f 20 25 73 20 61 6c movabs $0x6c61207325206f4e,%rax # "No %s al"
> ...
> 444674: 48 89 45 80 mov %rax,-0x80(%rbp)
> 444678: 48 b8 6c 6f 63 61 74 69 6f 6e movabs $0x6e6f697461636f6c,%rax # "location"
> 444682: 48 89 45 88 mov %rax,-0x78(%rbp)
> 444686: 48 b8 20 65 76 65 6e 74 73 20 movabs $0x2073746e65766520,%rax # " events "
> 444690: 66 44 89 55 c4 mov %r10w,-0x3c(%rbp)
> 444695: 48 89 45 90 mov %rax,-0x70(%rbp)
> 444699: 48 b8 66 6f 75 6e 64 2e 20 20 movabs $0x20202e646e756f66,%rax
>
> Make them all static so that the compiler just references objects in .rodata.
>

Ok, using dwarves's codiff tool:

$ codiff --functions /tmp/perf.before ~/bin/perf
builtin-sched.c:
cmd_sched | -48
1 function changed, 48 bytes removed, diff: -48

builtin-report.c:
cmd_report | -32
1 function changed, 32 bytes removed, diff: -32

builtin-kmem.c:
cmd_kmem | -64
build_alloc_func_list | -50
2 functions changed, 114 bytes removed, diff: -114

builtin-c2c.c:
perf_c2c__report | -390
1 function changed, 390 bytes removed, diff: -390

ui/browsers/header.c:
tui__header_window | -104
1 function changed, 104 bytes removed, diff: -104

/home/acme/bin/perf:
9 functions changed, 688 bytes removed, diff: -688

Thanks, applied.

- Arnaldo

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