[mythtv-users] Optimal RAM Allocation for Intel

Jim C jim_32766 at hotmail.com
Fri Oct 23 16:45:45 UTC 2015



On 10/23/2015 12:12 PM, Kirk Bocek wrote:
>
>
> On 10/23/2015 8:42 AM, Jim C wrote:
>> Info on the net from Intel indicates that their modern GPU
>> implementation like the HD 4600 is not dependent on reserved RAM (beyond
>> what small amount is needed at boot), and that the DVMT is more
>> important. The RAM for the GPU is dynamically allocated, based on need,
>> up to the limit set in the BIOS for DVMT. Provided there is sufficient
>> RAM to avoid contention when the dynamic allocation is needed the GPU
>> will get what it needs. In my case, if the DVMT limit is set to
>> "Maximum" the GPU could use up to 2GB of the 4GB available in my system.
>> I don't expect Mythtv's video requirements to ever reach the 2GB level,
>> so I've set the DVMT limit to Maximum to allow for best flexibility. The
>> next step down from Maximum was 250MB, and that seemed a little low.
>>
>> The data also discussed the benefits of the Intel Unified Memory
>> Architecture wherein the GPU has the same fast memory access bandwidth
>> as the CPU, reportedly 25GB/s for the HD 4600.
>>
>> Don't know if this is helpful to others - just passing it along for
>> consideration. Certainly, other CPU/GPU combinations could have
>> different specifics.
>>
>
> That's probably a more modern implementation that that present in the 
> ECS Liva: Bay Trail I think. Whatever memory you assign to video in 
> BIOS is actually removed from system memory. I have a fixed 1.5GB 
> available to Myth.
>
What you say about the ECS Liva makes sense. I look forward to trying 
one of those as a dedicated front end one day.

I think the motherboard plays a role in what can be set too. In one of 
the motherboards I have used recently there is no setting for DVMT, only 
a setting for shared memory as you have indicated. I think the DVMT 
exists in that board but is not adjustable. In the more recent 
motherboard I am using there are settings for shared memory and for 
DVMT. Based on the findings I was reporting I am leaving the shared 
memory setting at the factory default of 64MB and setting the DVMT to 
maximum. That seems to work well.


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