[vlc-devel] [PATCH] prefetch: remove read size, always request maximum

[Rémi Denis-Courmont]

Hi,

The access is free to return any non-zero size up to the requested read size, so the requested read size can never be too big. It can only ever be too small, and that's exactly why this patch made sense and still makes sense.

But if you need to worry about the read size, you've already lost. Small read size will cause bandwidth problems and large read size will cause latency problems.

Le 6 février 2020 12:33:55 GMT+02:00, Thomas Guillem <thomas at gllm.fr> a écrit :
>Hello,
>
>This commit and this one on vlc-3.0 :
>https://git.videolan.org/?p=vlc/vlc-3.0.git;a=commit;h=3dfa6d4ddd0922552e6575ded416f62b8ce828f5
>are making the smb2 module ultra slow, around 10 times slower.
>
>The read size requested by prefetch is really big. This make probing /
>seek ultra slow since a lot  of small read() are executed (reproduced
>with mkv and mp4).
>
>So, I have one big question: Is the smb2 module supposed to not listen
>to the size argument and always read a smaller size ?
>How can I decide the read size then ? Should this size be decided by
>the core of cache modules instead (like before) ?
>
>PS:  There is not the same problem with the libdsm module since the max
>read size is caped inside libdsm.
>
>On Fri, Apr 20, 2018, at 15:45, Thomas Guillem wrote:
>> 
>> On Fri, Apr 20, 2018, at 15:05, Rémi Denis-Courmont wrote:
>> > And I don't really want to hear a commit is dangerous from somebody
>that 
>> > backports stuff as lightly and quickly  as you have lately.
>> 
>> That is a bit close to false accusation IMHO.
>> 
>> > 
>> > This was sent for review, and it was *not* backported.
>> 
>> Yes and I was OK with it. It's just lately that I found out that this
>
>> commit might be dangerous.
>> Dangerous as changing the behavior of some access modules and maybe 
>> induce some new bugs (that are access related).
>> 
>> > -- 
>> > Envoyé de mon appareil Android avec Courriel K-9 Mail. Veuillez
>excuser 
>> > ma brièveté.
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-- 
Envoyé de mon appareil Android avec Courriel K-9 Mail. Veuillez excuser ma brièveté.
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