[mythtv-users] Combined FE/BE using USB for all I/O?

Simon Hobson linux at thehobsons.co.uk
Mon Aug 18 08:03:10 UTC 2014


Eric Sharkey <eric at lisaneric.org> wrote:

> And memory mapping doesn't add overhead.  In fact, just the opposite.
> 
> http://en.wikipedia.org/wiki/Memory-mapped_file
> 
> "The primary benefit of memory mapping a file is increasing I/O
> performance, especially when used on large files."

I'm guessing that some of these features might not have been around when the Myth devs were figuring out the problem. I don't know when memory mapped files appeared in the kernel, and I know Myth has been around a long time. Also, I suspect in the early days, a typical system didn't have a lot of RAM around, so memory mapping large files might not have been the panacea it appears to be now.

And Jean-Yves Avenard has now corrected some errors in my original description of how the system works.


> The MythTV devs have worked hard to get MythTV working well under many
> varied situations, but the Linux kernel developers have done the same.
> There are more kernel developers and the kernel code is more heavily
> stressed and tested than any particular application code.  Relying on
> the OS to do OS-like things like figuring out when to schedule
> particular disk writes is often the right call.

Yes, that makes sense.
I imagine the usual refrain of "code contributions always welcome" would apply. If it can be done better, as it sounds like it can, then it just needs someone who knows how to do that to write a bit of code for it. Like someone who does this sort of thing professionally ;-)



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