Michael Riepe schrieb:
> Hi!
>
> Dominik wrote:
>
>
>> First, I replaced POSIX_FADV_DONTNEED with POSIX_FADV_WILLNEED and did
>> some performace checks:
>>
>
> With the same arguments to posix_fadvise? That doesn't make sense
> because you're referencing the part of the file that has already been
> processed.
>
I replaced two lines with the "posix_fadvise(" command.
posix_fadvise(i->fd, 0, len, POSIX_FADV_NORMAL);
posix_fadvise(i->fd, 0, relpos, POSIX_FADV_NORMAL);
>
>> - Index generation takes quite the same time 1,1 GB in 17 seconds.
>> - Exporting on same hard disk is now done in 21 seconds instead of 34
>> seconds!
>> =>That's really good!
>>
>> Now, I tried a 4,3 GB file. (may memory has "only" 3,3 GB)
>> - Index generation takes now 103 seconds instead of 49 seconds. (that's
>> what is called "thrashing")
>> - Exporting takes 100% longer (288 sec instead of 148 seconds)
>> => this is definitely not OK.
>>
>
> Yep.
>
> [...]
>
>> Second (here is the interesting part ;-) )
>> I tried the option POSIX_FADV_NORMAL.
>>
>
> That would be the same as not calling posix_fadvise() at all. We already
> had that, and it wasn't good.
>
Really? On my machine it works excellent.
>
>> Now the system know itself and automatically(!) whether to hold the
>> video (...WILLNEED) or the don't hold the video (...DONTNEED) in memory.
>> => this ist the best parameter, because you get always the best perfomance!
>>
>
> Only if dvbcut is the only application running. Most of the time,
> however, it isn't. In particular, if you run a DVB recorder on the same
> machine, you are calling for big trouble - they need quite some amount
> of RAM for buffering and low latency (no swapping or thrashing).
> Otherwise, the receiver buffer will overflow, which punches holes of
> several seconds into your recorded video. That's worse than a VHS
> recorder with a damaged tape.
>
>
I know such problems on windows. "Do-nothing-during-recording"! (I had
often such holes in the video...)
and at least push the process priority to "high".
But I never habd such problem on linux.
When I record via DVB-T and vdr I can:
- browse
- copy files
- convert mpg->avi
- FTP upload
- dvbcut :-)
- everything else without any interruption of the video (and all on the
same hard disk!)
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