[FFmpeg-devel] AVDictionary vs. AVSet (AVDictionary2 approximation)

[Michael Niedermayer <michael@niedermayer.cc>]

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Hi

I just posted a AVSet implementation i wrote in the last 2 days (yes thats
why i did dissapear for the last 2 days)

My plan was to use that AVSet as basis for AVDictionary2 in case
benchmarks indicate that its worth it, so is it ?

with 3 entries (100000 runs)
AVDictionary    0.040sec
AVSet           0.027sec

with 5 entries (100000 runs)
AVDictionary    0.065sec
AVSet           0.042sec

with 10 entries (100000 runs)
AVDictionary    0.193sec
AVSet           0.087sec

with 100 entries (100000 runs)
AVDictionary    8.7  sec
AVSet           1.4  sec

with 1000 entries (1000 runs)
AVDictionary    8.0   sec
AVSet           0.240 sec

with 10000 entries (10 runs)
AVDictionary    7.2   sec
AVSet           0.042 sec


I was a bit surprised for the 3 and 5 entry case, maybe my benchmark is buggy or
AVSet is, but then AVDictionary is pretty bad with memory allocations

AVDictionary needs to strdup every key and value, needs to allocate
the AVDictionary itself and reallocs the entry array each time
thats 10 memory allocation related calls for adding 3 entries

while AVSet allocates the AVSet and then uses av_fast_realloc() for the array
and theres nothing else, the key/value goes in that array too


bechmark code used is below:


#if 0
    for (int runs = 0; runs < 100000; runs++) {
        AVSet *set = av_set_new(strcmp, NULL, NULL);
        for(int pass = 0; pass < 2; pass++) {
            unsigned r = 5;
            for(int i=0; i<100; i++) {
                r = r*123 + 7;
                char str[2*7] = "TESTXXTESTXX";
                str[4] = r;
                str[5] = r>>8;
                if(pass == 0) {
                    av_set_add(set, str, 2*7, 0);
                } else {
                    av_set_get(set, NULL, str, NULL);
                }
            }
        }
        av_set_free(&set);
    }
#else
    for (int runs = 0; runs < 100000; runs++) {
        AVDictionary *dict = NULL;
        for(int pass = 0; pass < 2; pass++) {
            unsigned r = 5;
            for(int i=0; i<100; i++) {
                r = r*123 + 7;
                char str[7] = "TEST";
                str[4] = r;
                str[5] = r>>8;
                if(pass == 0) {
                    av_dict_set(&dict, str, str, 0);
                } else {
                    av_dict_get(dict, str, NULL, 0);
                }
            }
        }
        av_dict_free(&dict);
    }
#endif


-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Good people do not need laws to tell them to act responsibly, while bad
people will find a way around the laws. -- Plato

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