4:02 a.m.
On (08/05/12 10:37), Arjan van de Ven wrote:
>>
>> + file.open("/sys/class/drm/card0/power/rc6_residency_ms", ios::in);
>> +
>> + if (file) {
>> + handle_i965_gpu();
>> + file.close();
>> + }
>> +
>
> side note: just wonder how much C++ stream with its heavy buffering, etc. is slower
> than stat(). I'll review and if it makes sense will probably prepare simple
stat()
> wrapper to lib.cpp
better to use access() than stat.
both have the fun of getting a bunch of low level system headers into C++
I'm sure that'll work most of the time, but for something as non-time critical as
this
I wonder how badly that is inviting trouble.
good point, that was just a small nit. I'm ok with one time fstream call.
>> +
>> + if (line_nr == 0)
>> + d = 100.0 - ratio * (rc6_after + rc6p_after + rc6pp_after - rc6_before -
rc6p_before - rc6pp_before);
>> + if (line_nr == 1)
>> + d = ratio * (rc6_after - rc6_before);
>> + if (line_nr == 2)
>> + d = ratio * (rc6p_after - rc6p_before);
>> + if (line_nr == 3)
>> + d = ratio * (rc6pp_after - rc6pp_before);
>> + if (line_nr >= 4 || line_nr < 0)
>> + return buffer;
>> +
>
> small side note /* someone will do it anyway :-) */:
> how about
>
> if (line_nr == 0)
> d = 100.0 - ratio * (rc6_after + rc6p_after + rc6pp_after - rc6_before -
rc6p_before - rc6pp_before);
> else if (line_nr == 1)
> d = ratio * (rc6_after - rc6_before);
> else if (line_nr == 2)
> d = ratio * (rc6p_after - rc6p_before);
> else if (line_nr == 3)
> d = ratio * (rc6pp_after - rc6pp_before);
> else if (line_nr >= 4 || line_nr < 0)
> return buffer;
well last time I looked at the disassembly for such a case, this generated worse code.
I'll admit that that was about 2 gcc versions ago though.
it's hard to tell nowadays, when GCC is free (and able) to generate even several
functions (not in this case,
of course) each of those will be specified for known parameter value: e.g. foo.part.1(),
foo.part.2(), foo.part.3()
for foo(1), foo(2) and foo(3) calls.
on my host (tested on dummy foo() routine) it's something like this (just for note)
gcc version 4.7.1 20120721
-O2
if ()
if ()
if ()
Dump of assembler code for function foo:
0x00000000004006b0 <+0>: cmp $0x1,%edi
0x00000000004006b3 <+3>: je 0x4006d8 <foo+40>
0x00000000004006b5 <+5>: cmp $0x2,%edi
0x00000000004006b8 <+8>: je 0x4006d8 <foo+40>
0x00000000004006ba <+10>: cmp $0x3,%edi
0x00000000004006bd <+13>: jne 0x4006f0 <foo+64>
0x00000000004006bf <+15>: mov %esi,%eax
0x00000000004006c1 <+17>: mov $0x4007bf,%edi
0x00000000004006c6 <+22>: imul %esi,%eax
0x00000000004006c9 <+25>: imul %esi,%eax
0x00000000004006cc <+28>: mov %eax,%esi
0x00000000004006ce <+30>: xor %eax,%eax
0x00000000004006d0 <+32>: jmpq 0x4004a0 <printf@plt>
0x00000000004006d5 <+37>: nopl (%rax)
0x00000000004006d8 <+40>: mov %esi,%eax
0x00000000004006da <+42>: imul %esi,%eax
0x00000000004006dd <+45>: mov %eax,%esi
0x00000000004006df <+47>: mov $0x4007bf,%edi
0x00000000004006e4 <+52>: xor %eax,%eax
0x00000000004006e6 <+54>: jmpq 0x4004a0 <printf@plt>
0x00000000004006eb <+59>: nopl 0x0(%rax,%rax,1)
0x00000000004006f0 <+64>: jbe 0x400706 <foo+86>
0x00000000004006f2 <+66>: lea (%rsi,%rsi,1),%eax
0x00000000004006f5 <+69>: mov $0x4007bf,%edi
0x00000000004006fa <+74>: imul %esi,%eax
0x00000000004006fd <+77>: mov %eax,%esi
0x00000000004006ff <+79>: xor %eax,%eax
0x0000000000400701 <+81>: jmpq 0x4004a0 <printf@plt>
0x0000000000400706 <+86>: xor %eax,%eax
0x0000000000400708 <+88>: jmp 0x4006dd <foo+45>
if ()
else if ()
else if ()
[..]
Dump of assembler code for function foo:
0x00000000004006b0 <+0>: xor %eax,%eax
0x00000000004006b2 <+2>: test %edi,%edi
0x00000000004006b4 <+4>: je 0x4006cd <foo+29>
0x00000000004006b6 <+6>: cmp $0x1,%edi
0x00000000004006b9 <+9>: je 0x4006e0 <foo+48>
0x00000000004006bb <+11>: cmp $0x2,%edi
0x00000000004006be <+14>: je 0x4006e0 <foo+48>
0x00000000004006c0 <+16>: cmp $0x3,%edi
0x00000000004006c3 <+19>: je 0x4006f8 <foo+72>
0x00000000004006c5 <+21>: jbe 0x4006cd <foo+29>
0x00000000004006c7 <+23>: lea (%rsi,%rsi,1),%eax
0x00000000004006ca <+26>: imul %esi,%eax
0x00000000004006cd <+29>: mov %eax,%esi
0x00000000004006cf <+31>: mov $0x4007bf,%edi
0x00000000004006d4 <+36>: xor %eax,%eax
0x00000000004006d6 <+38>: jmpq 0x4004a0 <printf@plt>
0x00000000004006db <+43>: nopl 0x0(%rax,%rax,1)
0x00000000004006e0 <+48>: mov %esi,%eax
0x00000000004006e2 <+50>: mov $0x4007bf,%edi
0x00000000004006e7 <+55>: imul %esi,%eax
0x00000000004006ea <+58>: mov %eax,%esi
0x00000000004006ec <+60>: xor %eax,%eax
0x00000000004006ee <+62>: jmpq 0x4004a0 <printf@plt>
0x00000000004006f3 <+67>: nopl 0x0(%rax,%rax,1)
0x00000000004006f8 <+72>: mov %esi,%eax
0x00000000004006fa <+74>: imul %esi,%eax
0x00000000004006fd <+77>: imul %esi,%eax
0x0000000000400700 <+80>: jmp 0x4006cd <foo+29>
both are not perfect, comparing to -Os case
if ()
if ()
if ()
Dump of assembler code for function foo:
0x0000000000400691 <+0>: cmp $0x1,%edi
0x0000000000400694 <+3>: jne 0x40069d <foo+12>
0x0000000000400696 <+5>: mov %esi,%eax
0x0000000000400698 <+7>: imul %esi,%eax
0x000000000040069b <+10>: jmp 0x4006b0 <foo+31>
0x000000000040069d <+12>: cmp $0x2,%edi
0x00000000004006a0 <+15>: je 0x400696 <foo+5>
0x00000000004006a2 <+17>: cmp $0x3,%edi
0x00000000004006a5 <+20>: jne 0x4006ae <foo+29>
0x00000000004006a7 <+22>: mov %esi,%eax
0x00000000004006a9 <+24>: imul %esi,%eax
0x00000000004006ac <+27>: jmp 0x4006b8 <foo+39>
0x00000000004006ae <+29>: xor %eax,%eax
0x00000000004006b0 <+31>: cmp $0x3,%edi
0x00000000004006b3 <+34>: jbe 0x4006bb <foo+42>
0x00000000004006b5 <+36>: lea (%rsi,%rsi,1),%eax
0x00000000004006b8 <+39>: imul %esi,%eax
0x00000000004006bb <+42>: mov %eax,%esi
0x00000000004006bd <+44>: mov $0x40077f,%edi
0x00000000004006c2 <+49>: xor %eax,%eax
0x00000000004006c4 <+51>: jmpq 0x4004a0 <printf@plt>
if ()
else if ()
else if ()
Dump of assembler code for function foo:
0x0000000000400691 <+0>: xor %eax,%eax
0x0000000000400693 <+2>: test %edi,%edi
0x0000000000400695 <+4>: je 0x4006b9 <foo+40>
0x0000000000400697 <+6>: cmp $0x1,%edi
0x000000000040069a <+9>: jne 0x4006a0 <foo+15>
0x000000000040069c <+11>: mov %esi,%eax
0x000000000040069e <+13>: jmp 0x4006b6 <foo+37>
0x00000000004006a0 <+15>: cmp $0x2,%edi
0x00000000004006a3 <+18>: je 0x40069c <foo+11>
0x00000000004006a5 <+20>: cmp $0x3,%edi
0x00000000004006a8 <+23>: jne 0x4006b1 <foo+32>
0x00000000004006aa <+25>: mov %esi,%eax
0x00000000004006ac <+27>: imul %esi,%eax
0x00000000004006af <+30>: jmp 0x4006b6 <foo+37>
0x00000000004006b1 <+32>: jbe 0x4006b9 <foo+40>
0x00000000004006b3 <+34>: lea (%rsi,%rsi,1),%eax
0x00000000004006b6 <+37>: imul %esi,%eax
0x00000000004006b9 <+40>: mov %eax,%esi
0x00000000004006bb <+42>: mov $0x40077f,%edi
0x00000000004006c0 <+47>: xor %eax,%eax
0x00000000004006c2 <+49>: jmpq 0x4004a0 <printf@plt>
-ss