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Old 01-Jan-2013, 21:47   #4
Andrew Lauritzen
Join Date: May 2004
Location: British Columbia, Canada
Posts: 2,275

Originally Posted by Davros View Post
Is this what you think amd is doing ?
I won't speculate much on that... it's hard to say without vtune-ing the relevant situation with driver symbols. I think there's a strong likelihood that the spikes are coming from the graphics driver, but beyond that I don't really have enough information to say.

Originally Posted by Lightman View Post
It was very visible in Crysis when looking into one direction after fraction of second FPS would rise, but sudden change of scenery (eg. looking away from sea towards build up area or forest) would initially drop FPS by quite some margin (only for fraction of second again but more than few frames).
Yeah it's definitely possible that this is due to JIT-style optimization; There are also cache warming effects though and sometimes the game has to do some streaming of its own when new stuff becomes visible.

Originally Posted by Lightman View Post
This also suggest that by increasing CPU speed we can expect these spikes to get smaller and eventually disappear.
The trouble is that a lot of this stuff is very single-threaded right now, so while increased frequency and IPC can help (which is why Intel CPUs tend to do better at games right now), more cores really does not. It's not trivial to multithread a lot of the runtime until GPUs can accept significantly more interesting command streams, ideally submitted in parallel. But of course there's some slightly skewed economies with discrete GPUs that discourage this, since when GPUs are benchmarked vs. one another they are typically done with the fastest CPUs available. And of course they are benchmarked with average FPS...

Power-constrained integrated CPU/GPUs should change this equation somewhat, as lightening the CPU workload (driver, etc) can directly affect the power/frequency available to the GPU.

Originally Posted by Lightman View Post
I wonder about another possibility when CPU is so much ahead of GPU that it idles in between frames and goes into C states, can this affect frame rendering enough to matter?
I doubt this has a large effect to be honest, but I don't remember the details of the latencies involved in each solution. But again, anything affecting power definitely gets interesting on integrated SoCs in the future.
The content of this message is my personal opinion only.

Last edited by Andrew Lauritzen; 01-Jan-2013 at 22:00.
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