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When GPU needs more scratch it requests from the runtime. In the method to wait for response, a dmaReadVirt is called with the same method as the callback with zero delay. This means that effectively there is an infinite loop in the event queue if the scratch setup is not successful on the first attempt. In the case of GPUFS, it is never successfully instantly so a delay must be added. Without added delay, the host CPU is never scheduled to make progress setting up more scratch space. The value 1e9 is choosen to match the KVM quantum and hopefully give KVM a chance to schedule an event. For reference, the driver timeout is 200ms so this is still fairly aggressive checking of the signal response. This value is also balanced around the GPUCommandProc DPRINTF to prevent the print in this method from overwhelming debug output. Change-Id: I0e0e1d75cd66f7c47815b13a4bfc3c0188e16220 Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/61651 Tested-by: kokoro <noreply+kokoro@google.com> Reviewed-by: Matt Sinclair <mattdsinclair@gmail.com> Maintainer: Matt Sinclair <mattdsinclair@gmail.com>
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11 KiB