Re: [linux-audio-dev] DRI + Jack conflict?

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Subject: Re: [linux-audio-dev] DRI + Jack conflict?
From: Vincent Touquet (vincent.touquet_AT_pandora.be)
Date: Tue Feb 10 2004 - 14:32:43 EET


On Mon, Feb 09, 2004 at 07:32:35PM -0500, Paul Davis wrote:
>its a basic problem with real time software, the POSIX API etc.
>JACK tries to lock *all* the process memory.

This is to ensure that nothing gets swapped out, right ?
Else it is very hard to ensure real time performance ?
(sorry for being somewhat ignorant in this matter).

>POSIX doesn't offer any
>APIs that would allow us to lock only the parts we need locked without
>a lot of impossibly ugly, non-portable kludgery.
>the part that needs
>locking consists of any memory that will be touched by the code run in
>the JACK-managed "audio" thread.
>the implementation of DRI by certain video interface drivers means
>that we end up trying to lock the video memory as well, and this tends
>to fail for various reasons.

Is this faillure due to the nature of the memory that we are trying to lock ?
Or is the problem that we try to lock the same part of memory multiple times ?

>its not what to do about this. the most obvious answer is "don't try
>to run real-time software on systems with these video drivers
>installed". i know its not very satisfactory, but its all we have for
>now.

Would the less obvious answer consist of one of the following ?:
- change the video drivers (at least the ones that are source based)
- do something at the API level, so we can lock selectively

>From what I can gather the optimal solution would be an API that
can give us what we want (only locking the memory that gets touched
by the audio thread and nothing else), but obviously this goes beyond
the scope of jack alone ?

Would you consider implementing a work around (aka non portable kludgery)
a waste of time ?

regards,

v


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