gcc -Ofast -pg錯誤的gprof結果
[英]wrong gprof results with gcc -Ofast -pg
問題描述
我看到了gcc -pg和gprof奇怪分析結果。
我找不到更好/更小的重現方法，所以我將實際問題鏈接到實際的代碼上。
我在這里使用代碼，用make prof構建gprof分析結果
我注意到幾個錯誤，主要是：
- 顯示一個甚至不應該調用的
shape_stream_test函數被ai_best_move_rec大量調用，並占用了自身運行時間的15％ - 由
ai_best_move_rec合法調用的其他函數，例如grid_block_remove，grid_cpy，grid_new甚至都不會顯示為子級
實際教授數據：
Flat profile:
Each sample counts as 0.01 seconds.
% cumulative self self total
time seconds seconds calls ms/call ms/call name
53.92 4.00 4.00 4231936 0.00 0.00 grid_eval
13.62 5.01 1.01 4467368 0.00 0.00 shape_stream_test
6.88 5.52 0.51 4690742 0.00 0.00 grid_block_center_top
6.07 5.97 0.45 4521016 0.00 0.00 grid_block_valid
5.80 6.40 0.43 4467368 0.00 0.00 grid_block_add
3.37 6.65 0.25 4467368 0.00 0.00 grid_block_drop
2.02 6.80 0.15 35 4.29 209.20 ai_best_move_rec
1.95 6.95 0.15 235469 0.00 0.00 grid_init
1.75 7.08 0.13 9212461 0.00 0.00 block_extreme
1.48 7.19 0.11 4467402 0.00 0.00 block_move
0.94 7.26 0.07 1654899 0.00 0.00 block_get
0.54 7.30 0.04 block_crust_get
0.40 7.33 0.03 grid_block_set_color
0.27 7.35 0.02 4467368 0.00 0.00 grid_block_remove
0.27 7.37 0.02 235501 0.00 0.00 block_new
0.27 7.39 0.02 grid_block_intersects
0.20 7.40 0.02 235469 0.00 0.00 grid_new
0.13 7.41 0.01 235467 0.00 0.00 shape_stream_peek
0.13 7.42 0.01 drop_amount
0.00 7.42 0.00 621 0.00 0.00 grid_clear_lines
0.00 7.42 0.00 587 0.00 0.00 grid_cpy
0.00 7.42 0.00 35 0.00 0.00 grid_print
0.00 7.42 0.00 34 0.00 0.00 block_init
0.00 7.42 0.00 34 0.00 0.00 block_print
0.00 7.42 0.00 34 0.00 0.00 game_move_print
0.00 7.42 0.00 34 0.00 0.00 grid_apply_moves
0.00 7.42 0.00 34 0.00 0.00 shape_stream_pop
0.00 7.42 0.00 7 0.00 0.00 shape_new
0.00 7.42 0.00 1 0.00 0.00 shape_stream_new
% the percentage of the total running time of the
time program used by this function.
cumulative a running sum of the number of seconds accounted
seconds for by this function and those listed above it.
self the number of seconds accounted for by this
seconds function alone. This is the major sort for this
listing.
calls the number of times this function was invoked, if
this function is profiled, else blank.
self the average number of milliseconds spent in this
ms/call function per call, if this function is profiled,
else blank.
total the average number of milliseconds spent in this
ms/call function and its descendents per call, if this
function is profiled, else blank.
name the name of the function. This is the minor sort
for this listing. The index shows the location of
the function in the gprof listing. If the index is
in parenthesis it shows where it would appear in
the gprof listing if it were to be printed.
Copyright (C) 2012-2014 Free Software Foundation, Inc.
Copying and distribution of this file, with or without modification,
are permitted in any medium without royalty provided the copyright
notice and this notice are preserved.
Call graph (explanation follows)
granularity: each sample hit covers 2 byte(s) for 0.13% of 7.42 seconds
index % time self children called name
<spontaneous>
[1] 98.7 0.00 7.32 ai_test [1]
0.15 7.17 35/35 ai_best_move_rec [2]
0.00 0.00 34/34 grid_apply_moves [21]
0.00 0.00 2/235469 grid_new [9]
0.00 0.00 35/35 grid_print [24]
0.00 0.00 34/34 game_move_print [27]
0.00 0.00 34/34 shape_stream_pop [28]
0.00 0.00 1/1 shape_stream_new [30]
-----------------------------------------------
235432 ai_best_move_rec [2]
0.15 7.17 35/35 ai_test [1]
[2] 98.7 0.15 7.17 35+235432 ai_best_move_rec [2]
4.00 0.00 4231936/4231936 grid_eval [3]
1.01 0.00 4467368/4467368 shape_stream_test [4]
0.51 0.11 4690742/4690742 grid_block_center_top [5]
0.45 0.09 4521016/4521016 grid_block_valid [6]
0.43 0.00 4467368/4467368 grid_block_add [7]
0.25 0.00 4467368/4467368 grid_block_drop [8]
0.02 0.15 235467/235469 grid_new [9]
0.11 0.00 4467368/4467402 block_move [12]
0.02 0.00 4467368/4467368 grid_block_remove [16]
0.02 0.00 235467/235501 block_new [17]
0.01 0.00 235467/235467 shape_stream_peek [19]
0.00 0.00 587/587 grid_cpy [23]
0.00 0.00 587/621 grid_clear_lines [22]
235432 ai_best_move_rec [2]
-----------------------------------------------
4.00 0.00 4231936/4231936 ai_best_move_rec [2]
[3] 53.9 4.00 0.00 4231936 grid_eval [3]
-----------------------------------------------
1.01 0.00 4467368/4467368 ai_best_move_rec [2]
[4] 13.6 1.01 0.00 4467368 shape_stream_test [4]
-----------------------------------------------
0.51 0.11 4690742/4690742 ai_best_move_rec [2]
[5] 8.4 0.51 0.11 4690742 grid_block_center_top [5]
0.07 0.00 4690742/9212461 block_extreme [11]
0.04 0.00 1056160/1654899 block_get [13]
-----------------------------------------------
0.45 0.09 4521016/4521016 ai_best_move_rec [2]
[6] 7.3 0.45 0.09 4521016 grid_block_valid [6]
0.06 0.00 4521016/9212461 block_extreme [11]
0.03 0.00 598739/1654899 block_get [13]
-----------------------------------------------
0.43 0.00 4467368/4467368 ai_best_move_rec [2]
[7] 5.8 0.43 0.00 4467368 grid_block_add [7]
-----------------------------------------------
0.25 0.00 4467368/4467368 ai_best_move_rec [2]
[8] 3.4 0.25 0.00 4467368 grid_block_drop [8]
0.00 0.00 635/9212461 block_extreme [11]
-----------------------------------------------
0.00 0.00 2/235469 ai_test [1]
0.02 0.15 235467/235469 ai_best_move_rec [2]
[9] 2.2 0.02 0.15 235469 grid_new [9]
0.15 0.00 235469/235469 grid_init [10]
-----------------------------------------------
0.15 0.00 235469/235469 grid_new [9]
[10] 2.0 0.15 0.00 235469 grid_init [10]
-----------------------------------------------
0.00 0.00 68/9212461 grid_apply_moves [21]
0.00 0.00 635/9212461 grid_block_drop [8]
0.06 0.00 4521016/9212461 grid_block_valid [6]
0.07 0.00 4690742/9212461 grid_block_center_top [5]
[11] 1.8 0.13 0.00 9212461 block_extreme [11]
-----------------------------------------------
0.00 0.00 34/4467402 grid_apply_moves [21]
0.11 0.00 4467368/4467402 ai_best_move_rec [2]
[12] 1.5 0.11 0.00 4467402 block_move [12]
-----------------------------------------------
0.03 0.00 598739/1654899 grid_block_valid [6]
0.04 0.00 1056160/1654899 grid_block_center_top [5]
[13] 0.9 0.07 0.00 1654899 block_get [13]
-----------------------------------------------
<spontaneous>
[14] 0.5 0.04 0.00 block_crust_get [14]
-----------------------------------------------
<spontaneous>
[15] 0.4 0.03 0.00 grid_block_set_color [15]
-----------------------------------------------
0.02 0.00 4467368/4467368 ai_best_move_rec [2]
[16] 0.3 0.02 0.00 4467368 grid_block_remove [16]
-----------------------------------------------
0.00 0.00 34/235501 grid_apply_moves [21]
0.02 0.00 235467/235501 ai_best_move_rec [2]
[17] 0.3 0.02 0.00 235501 block_new [17]
-----------------------------------------------
<spontaneous>
[18] 0.3 0.02 0.00 grid_block_intersects [18]
-----------------------------------------------
0.01 0.00 235467/235467 ai_best_move_rec [2]
[19] 0.1 0.01 0.00 235467 shape_stream_peek [19]
-----------------------------------------------
<spontaneous>
[20] 0.1 0.01 0.00 drop_amount [20]
-----------------------------------------------
0.00 0.00 34/34 ai_test [1]
[21] 0.0 0.00 0.00 34 grid_apply_moves [21]
0.00 0.00 34/235501 block_new [17]
0.00 0.00 68/9212461 block_extreme [11]
0.00 0.00 34/4467402 block_move [12]
0.00 0.00 34/34 block_init [25]
0.00 0.00 34/621 grid_clear_lines [22]
-----------------------------------------------
0.00 0.00 34/621 grid_apply_moves [21]
0.00 0.00 587/621 ai_best_move_rec [2]
[22] 0.0 0.00 0.00 621 grid_clear_lines [22]
-----------------------------------------------
0.00 0.00 587/587 ai_best_move_rec [2]
[23] 0.0 0.00 0.00 587 grid_cpy [23]
-----------------------------------------------
0.00 0.00 35/35 ai_test [1]
[24] 0.0 0.00 0.00 35 grid_print [24]
-----------------------------------------------
0.00 0.00 34/34 grid_apply_moves [21]
[25] 0.0 0.00 0.00 34 block_init [25]
-----------------------------------------------
0.00 0.00 34/34 game_move_print [27]
[26] 0.0 0.00 0.00 34 block_print [26]
-----------------------------------------------
0.00 0.00 34/34 ai_test [1]
[27] 0.0 0.00 0.00 34 game_move_print [27]
0.00 0.00 34/34 block_print [26]
-----------------------------------------------
0.00 0.00 34/34 ai_test [1]
[28] 0.0 0.00 0.00 34 shape_stream_pop [28]
-----------------------------------------------
0.00 0.00 7/7 shapes_read [68]
[29] 0.0 0.00 0.00 7 shape_new [29]
-----------------------------------------------
0.00 0.00 1/1 ai_test [1]
[30] 0.0 0.00 0.00 1 shape_stream_new [30]
-----------------------------------------------
This table describes the call tree of the program, and was sorted by
the total amount of time spent in each function and its children.
Each entry in this table consists of several lines. The line with the
index number at the left hand margin lists the current function.
The lines above it list the functions that called this function,
and the lines below it list the functions this one called.
This line lists:
index A unique number given to each element of the table.
Index numbers are sorted numerically.
The index number is printed next to every function name so
it is easier to look up where the function is in the table.
% time This is the percentage of the `total' time that was spent
in this function and its children. Note that due to
different viewpoints, functions excluded by options, etc,
these numbers will NOT add up to 100%.
self This is the total amount of time spent in this function.
children This is the total amount of time propagated into this
function by its children.
called This is the number of times the function was called.
If the function called itself recursively, the number
only includes non-recursive calls, and is followed by
a `+' and the number of recursive calls.
name The name of the current function. The index number is
printed after it. If the function is a member of a
cycle, the cycle number is printed between the
function's name and the index number.
For the function's parents, the fields have the following meanings:
self This is the amount of time that was propagated directly
from the function into this parent.
children This is the amount of time that was propagated from
the function's children into this parent.
called This is the number of times this parent called the
function `/' the total number of times the function
was called. Recursive calls to the function are not
included in the number after the `/'.
name This is the name of the parent. The parent's index
number is printed after it. If the parent is a
member of a cycle, the cycle number is printed between
the name and the index number.
If the parents of the function cannot be determined, the word
`<spontaneous>' is printed in the `name' field, and all the other
fields are blank.
For the function's children, the fields have the following meanings:
self This is the amount of time that was propagated directly
from the child into the function.
children This is the amount of time that was propagated from the
child's children to the function.
called This is the number of times the function called
this child `/' the total number of times the child
was called. Recursive calls by the child are not
listed in the number after the `/'.
name This is the name of the child. The child's index
number is printed after it. If the child is a
member of a cycle, the cycle number is printed
between the name and the index number.
If there are any cycles (circles) in the call graph, there is an
entry for the cycle-as-a-whole. This entry shows who called the
cycle (as parents) and the members of the cycle (as children.)
The `+' recursive calls entry shows the number of function calls that
were internal to the cycle, and the calls entry for each member shows,
for that member, how many times it was called from other members of
the cycle.
Copyright (C) 2012-2014 Free Software Foundation, Inc.
Copying and distribution of this file, with or without modification,
are permitted in any medium without royalty provided the copyright
notice and this notice are preserved.
Index by function name
[2] ai_best_move_rec [21] grid_apply_moves [3] grid_eval
[14] block_crust_get [7] grid_block_add [10] grid_init
[11] block_extreme [5] grid_block_center_top [9] grid_new
[13] block_get [8] grid_block_drop [24] grid_print
[25] block_init [18] grid_block_intersects [29] shape_new
[12] block_move [16] grid_block_remove [30] shape_stream_new
[17] block_new [15] grid_block_set_color [19] shape_stream_peek
[26] block_print [6] grid_block_valid [28] shape_stream_pop
[20] drop_amount [22] grid_clear_lines [4] shape_stream_test
[27] game_move_print [23] grid_cpy
后來我發現我正在組合-Ofast和-pg標志，並且刪除-Ofast可以解決上述問題。
我的問題是：
這兩個標志不兼容嗎？ 我在文檔中找不到任何此類警告
如果它們不兼容，這是gcc錯誤嗎？
如何解決此問題，以查看與最積極的優化相匹配的性能分析結果，以免浪費時間優化錯誤的代碼？
1 個解決方案
解決方案1
1 已采納 2016-08-16 12:54:00
你要速度吧？ -Ofast僅在調用堆棧的底部-Ofast 。 它無法解決僅您可以解決的問題。 這只會使他們更難找到。 首先關閉優化器並修復您可以修復的問題。 這是一些人如何做的例子。 當您盡可能地做到這一點時，請打開優化器並使其發揮作用。
小火焰：)很多人說配置未優化的代碼是浪費時間，但是他們從不說原因 。 他們在演講廳里聽到了這個聲音，在博客上看了它，或者從stackoverflow上聽到了這個聲音，而這個人的明確權限使他不必給出理由。
我認為這是一廂情願的情況：我的代碼基本上是完美的，因此可以加快其速度的唯一方法是運行編譯器的優化器。 然后，當探查器顯示無法加快速度時，這顯然是正確的，為我加油！
為了回應評論而添加：讓我有點離題（對不起）。 我了解人們可以仔細檢查代碼，花精力在數據表示上，內聯一些函數，進行其他高級優化，並以此來衡量加速。 大。 但是，如果您每次更改代碼的原因只是查看並思考代碼，那么按照您的想法進行培訓，這仍然是一種猜測。 猜測可能是正確的，但是您應該問的問題是“我錯過了什么？” 和“我如何找到它？”
我和很多人使用的方法是隨機暫停 。 它唯一需要的工具是調試器，例如GDB或任何IDE。 它與概要分析的不同之處在於，它直接定位不必要的計算，而不是進行測量並依靠您來解密，過濾噪聲，查看特定例程並在其中進行搜尋。 它告訴您特定的代碼行和特定的數據，程序在做什么以及為什么這樣做。 然后，您可以詢問是否有一種不那么浪費的方法來進行操作，並且有機會存在。 什么它不會做的就是告訴你時間的精確分數-你只得到一個非常粗略測量。 它所做的確定問題。 您可能會認為您當然不能依靠這種不准確的方法，並且如果您僅在一個樣本上看到問題，那就是正確的。 但是，如果您在一個以上的樣本上看到它，那您就會知道它很大，而一次以上看到的整體樣本越少，它就越大。 以下是其背后的統計信息。 關鍵在於：這將發現任何探查器將發現的任何問題，以及更多。
然后，當您發現並解決一個問題時，您可以再次執行所有操作，因為刪除一個問題會放大其余的問題。 這樣，您就可以“加速”加速，直到無法再加速為止。 如本例所示，這就是獲得最大速度的方法 。 然后，請-Ofast使用-Ofast 。
為什么 GCC -Ofast 會使程序出錯，但只有在它打印兩次結果時才會出錯？
[英]Why GCC -Ofast makes the program wrong but only when it prints the result twice?
使用 gcc 上的 -Ofast 標志，分解數學表達式會影響速度嗎？
[英]With the -Ofast flag on gcc, does breaking down a math expression affect speed?
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