From: "softworkz ." <softworkz-at-hotmail.com@ffmpeg.org>
To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
Subject: Re: [FFmpeg-devel] AVDictionary vs. AVSet (AVDictionary2 approximation)
Date: Mon, 14 Apr 2025 12:40:11 +0000
Message-ID: <BN0P223MB0358D7E3367462AA4EF9B744BAB32@BN0P223MB0358.NAMP223.PROD.OUTLOOK.COM> (raw)
In-Reply-To: <20250414113328.GM4991@pb2>
> -----Original Message-----
> From: ffmpeg-devel <ffmpeg-devel-bounces@ffmpeg.org> On Behalf Of
> Michael Niedermayer
> Sent: Montag, 14. April 2025 13:33
> To: FFmpeg development discussions and patches <ffmpeg-
> devel@ffmpeg.org>
> Subject: [FFmpeg-devel] AVDictionary vs. AVSet (AVDictionary2
> approximation)
>
> 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
>
>
> --
Hi Michael,
what's not quite realistic is that all keys are starting with the same 4 characters. This affects the lookups of course - and probably (maybe) not equally for both sides.
Doesn't the code create duplicate keys (at least when it gets > 65536 it will for sure) ?
So, I think, the keys should be completely random (all chars).
I would also check whether the lookups are successful (just to be sure).
Best,
sw
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next prev parent reply other threads:[~2025-04-14 12:40 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-04-14 11:33 Michael Niedermayer
2025-04-14 12:40 ` softworkz . [this message]
2025-04-14 13:02 ` softworkz .
2025-04-15 19:11 ` Michael Niedermayer
2025-04-15 20:36 ` Michael Niedermayer
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