Replaces old and simple usages of std::atomic<bool> with Common::Flag
(which was introduced after the initial usage), so it's clear that
the variable is a flag and because Common::Flag is well tested.
This also replaces the ready logic in WiimoteReal with Common::Event
since it was basically just unnecessarily reimplementing Common::Event.
CBoot::BootUp() did call CoreTiming::Advance which itself blocks on the GPU,
but the GPU thread wasn't started already. This commit moves the SyncGPU
initialization into the Fifo.cpp file and call it after BootUp().
The new implementation has 3 options:
SyncGpuMaxDistance
SyncGpuMinDistance
SyncGpuOverclock
The MaxDistance controlls how many CPU cycles the CPU is allowed to be in front
of the GPU. Too low values will slow down extremly, too high values are as
unsynchronized and half of the games will crash.
The -MinDistance (negative) set how many cycles the GPU is allowed to be in
front of the CPU. As we are used to emulate an infinitiv fast GPU, this may be
set to any high (negative) number.
The last parameter is to hack a faster (>1.0) or slower(<1.0) GPU. As we don't
emulate GPU timing very well (eg skip the timings of the pixel stage completely),
an overclock factor of ~0.5 is often much more accurate than 1.0
This was causing a race condition where the "absurdly large aux buffer"
panic alert would be triggered in the last bit of fifo processing on the
CPU thread in deterministic mode (i.e. netplay). SyncGPU is supposed to
move the auxiliary queue data to the beginning of the containing buffer
so we don't have to deal with wraparound; if GpuRunningState is false,
however, it just returns, because it's set to false by another thread -
thus it doesn't know whether RunGpuLoop is still executing (in which
case it can't just reset the pointers, because it may still be using the
buffer) or not (in which case the condition variable it normally waits
for to avoid the previous problem will never be signaled). However,
SyncGPU's caller PushFifoAuxBuffer wasn't aware of this, so if the
buffer was filling at just the right time, it'd stay full and that
function would complain that it was about to overflow it. Similar
problem with ReadDataFromFifoOnCPU afaik. Fix this by returning early
from those as well; other callers of SyncGPU should be safe. A
*slightly* cleaner alternative would be giving the CPU thread a way to
tell when RunGpuLoop has actually exited, but whatever, this works.
Previously we had decided to busy loop on systems due to Windows' scheduler being terrible and moving us around CPU cores when we yielded.
Along with context switching being a hot spot.
We had decided to busy loop in these situations instead, which allows us greater CPU performance on the video thread.
This can be attributed to multiple things, CPU not downclocking while busy looping, context switches happening less often, yielding taking more time
than a busy loop, etc.
One thing we had considered when moving over to a busy loop is the issues that dual core systems would now face due to Dolphin eating all of their CPU
resources. Effectively we are starving a dual core system of any time to do anything else due to the CPU thread always being pinned at 100% and then
the GPU thread also always at 100% just spinning around. We noted the potential for a performance regression, but dismissed it as most computers are
now becoming quad core or higher.
This change in particular has performance advantages on the dual core Nvidia Denver due to its architecture being nonstandard. If both CPU cores are
maxed out, the CPU can't effectively take any idle time to recompile host code blocks to its native VLIW architecture.
It can still do so, but it does less frequently which results in performance issues in Dolphin due to most code just running through the in-order
instruction decoder instead of the native VLIW architecture.
In one particular example, yielding moves the performance from 35-40FPS to 50-55FPS. So it is far more noticeable on Denver than any other system.
Of course once a triple or quad core Denver system comes out this will no longer be an issue on this architecture since it'll have a free core to do
all of this work.
degasus