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When things go wrong, the GPU is capable of quickly generating millions of faulting translation requests per second. When that happens, in the stall-on-fault model each access will stall until it wins the race to signal the fault and then the RESUME register is written. This slows processing page faults to a crawl as the GPU can generate faults much faster than the CPU can acknowledge them. It also means that all available resources in the SMMU are saturated waiting for the stalled transactions, so that other transactions such as transactions generated by the GMU, which shares translation resources with the GPU, cannot proceed. This causes a GMU watchdog timeout, which leads to a failed reset because GX cannot collapse when there is a transaction pending and a permanently hung GPU. On older platforms with qcom,smmu-v2, it seems that when one transaction is stalled subsequent faulting transactions are terminated, which avoids this problem, but the MMU-500 follows the spec here. To work around these problems, disable stall-on-fault as soon as we get a page fault until a cooldown period after pagefaults stop. This allows the GMU some guaranteed time to continue working. We only use stall-on-fault to halt the GPU while we collect a devcoredump and we always terminate the transaction afterward, so it's fine to miss some subsequent page faults. We also keep it disabled so long as the current devcoredump hasn't been deleted, because in that case we likely won't capture another one if there's a fault. After this commit HFI messages still occasionally time out, because the crashdump handler doesn't run fast enough to let the GMU resume, but the driver seems to recover from it. This will probably go away after the HFI timeout is increased. Signed-off-by: Connor Abbott <cwabbott0@gmail.com> Reviewed-by: Rob Clark <robdclark@gmail.com> Patchwork: https://patchwork.freedesktop.org/patch/654891/ Signed-off-by: Rob Clark <robin.clark@oss.qualcomm.com> |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.