I am using the odroid XU3 board. It has the Samsung Exynos5422 SoC. The SoC has BigLittle CPUs and the Arm Mali T628 MP6 GPU. I would like to run the CPU and the GPU in parallel on different sections of the array that I am processing. Currently to enforce coherency I have to use clEnqueueMapBuffer and clEnqueueUnmapMemObject. Usage of these OpenCL functions gives a performance degradation and due to this running the CPU and GPU in parallel becomes pointless. I have the following questions.
1) Are the caches of the ARM CPU and the GPU on this SoC coherent ?
2) The GPU shows up as two devices in OpenCL. Are these GPUs cache coherent ?3) Is there anyway to enforce coherency other than using MapBuffer and UnmapMemObject CL functions ?
To clarify:
Graphical applications, such as those using OpenGL ES, do not need to worry about the two clusters. Their applications will run on all 6 cores (T628-MP6) without modification.
Compute applications, such as those using OpenCL, do need to worry about the two clusters. If they do not modify their application to utilise both CL devices in parallel, then they will only utilise 4 out of the 6 cores. With modification however, they can run on all 6 cores.
Kind Regards,
Michael McGeagh
very thank you for your reply, now everything is clear. But do you can not modified drivers to operate all 6 cores for OpenCL?
mali t628 mp6 with which frequency can work?
But do you can not modified drivers to operate all 6 cores for OpenCL?
No; you'd need hardware memory coherency between the two core clusters to make it work transparently, which Mali-T620 doesn't support. Only the application has enough knowledge to know how to split the work safely across the two devices, so that's why we expose it as two separate OpenCL devices to the application - you can use all 6 cores, it just takes a little more effort .
As mcgeagh has pointed out, we added the hardware support to the newer Mali GPUs (Anything in Mali-T700 series onwards), so in newer chipsets this is no longer an issue.
ARM just license the GPU IP to our silicon partners; the achievable top frequency depends on many aspects of physical implementation. This question is best aimed at the supplier of a specific chip.
HTH, Pete
hmm but mali-t720 i think it also has this problem?
link: http://www.arm.com/products/multimedia/mali-gpu/high-area-efficiency/mali-t720.php
Mali-T720 is designed for low and mid-end devices which want to save silicon area; I'm not aware of any implementation with more than 4 cores.
thank you very much for your answer.mali t628 mp6 with which frequency can work?ARM just license the GPU IP to our silicon partners; the achievable top frequency depends on many aspects of physical implementation. This question is best aimed at the supplier of a specific chip.
thank you very much for your answer.
but whether mali-t628 mp6 can work at 695 mhz?
Hi kubussz
I will repeat what peterharris has already said:
We cannot answer that question as it is not controlled by us. Please ask your silicon provider of your targeted SoC to see if they can run the GPU at that clock frequency.
thank you for your answer.