使用cachegrind和callgrind进行不同的读写计数

Question

我正在使用Cachegrind,Callgrind和Gem5进行一些实验.我注意到一些访问被计为cachegrind的读取,如callgrind的写入以及gem5的读取和写入.

我们来看一个非常简单的例子:

int main() {
    int i, l;

    for (i = 0; i < 1000; i++) {
        l++;
        l++;
        l++;
        l++;
        l++;
        l++;
        l++;
        l++;
        l++;
        l++;
        ... (100 times)
     }
 }

我编译:

gcc ex.c --static -o ex

所以基本上,根据asm文件,addl $1, -8(%rbp)执行100,000次.由于它既是读取也是写入,我期待100k读取和100k写入.但是,cachegrind只将它们计为read,而callgrind只计为write.

 % valgrind --tool=cachegrind --I1=512,8,64 --D1=512,8,64
--L2=16384,8,64 ./ex
==15356== Cachegrind, a cache and branch-prediction profiler
==15356== Copyright (C) 2002-2012, and GNU GPL'd, by Nicholas Nethercote et al.
==15356== Using Valgrind-3.8.1 and LibVEX; rerun with -h for copyright info
==15356== Command: ./ex
==15356== 
--15356-- warning: L3 cache found, using its data for the LL simulation.
==15356== 
==15356== I   refs:      111,535
==15356== I1  misses:        475
==15356== LLi misses:        280
==15356== I1  miss rate:    0.42%
==15356== LLi miss rate:    0.25%
==15356== 
==15356== D   refs:      104,894  (103,791 rd   + 1,103 wr)
==15356== D1  misses:        557  (    414 rd   +   143 wr)
==15356== LLd misses:        172  (     89 rd   +    83 wr)
==15356== D1  miss rate:     0.5% (    0.3%     +  12.9%  )
==15356== LLd miss rate:     0.1% (    0.0%     +   7.5%  )
==15356== 
==15356== LL refs:         1,032  (    889 rd   +   143 wr)
==15356== LL misses:         452  (    369 rd   +    83 wr)
==15356== LL miss rate:      0.2% (    0.1%     +   7.5%  )

-

 % valgrind --tool=callgrind --I1=512,8,64 --D1=512,8,64
--L2=16384,8,64 ./ex
==15376== Callgrind, a call-graph generating cache profiler
==15376== Copyright (C) 2002-2012, and GNU GPL'd, by Josef Weidendorfer et al.
==15376== Using Valgrind-3.8.1 and LibVEX; rerun with -h for copyright info
==15376== Command: ./ex
==15376== 
--15376-- warning: L3 cache found, using its data for the LL simulation.
==15376== For interactive control, run 'callgrind_control -h'.
==15376== 
==15376== Events    : Ir Dr Dw I1mr D1mr D1mw ILmr DLmr DLmw
==15376== Collected : 111532 2777 102117 474 406 151 279 87 85
==15376== 
==15376== I   refs:      111,532
==15376== I1  misses:        474
==15376== LLi misses:        279
==15376== I1  miss rate:    0.42%
==15376== LLi miss rate:    0.25%
==15376== 
==15376== D   refs:      104,894  (2,777 rd + 102,117 wr)
==15376== D1  misses:        557  (  406 rd +     151 wr)
==15376== LLd misses:        172  (   87 rd +      85 wr)
==15376== D1  miss rate:     0.5% ( 14.6%   +     0.1%  )
==15376== LLd miss rate:     0.1% (  3.1%   +     0.0%  )
==15376== 
==15376== LL refs:         1,031  (  880 rd +     151 wr)
==15376== LL misses:         451  (  366 rd +      85 wr)
==15376== LL miss rate:      0.2% (  0.3%   +     0.0%  )

有人能给我一个合理的解释吗？我是否应该认为实际上有~100k读取和~100k写入(即addl的2次缓存访问)？

Answer 1

callgrind 默认情况下不进行全缓存模拟。请参阅此处： http: //valgrind.org/docs/manual/cl-manual.html#cl-manual.options.cachesimulation

要启用数据读取访问，您需要为 callgrind 添加 --cache-sim=yes 。话虽如此，为什么还要在这段代码上使用 callgrind 呢？没有单个函数调用（这就是 callgrind 的用途）