Am 17.06.24 um 17:35 schrieb Xi Ruoyao:
On Mon, 2024-06-17 at 22:30 +0800, Icenowy Zheng wrote:
Two consecutive writes to the same bus address are perfectly legal
the PCIe specification and can happen all the time, even without this
specific hw workaround.
Yes I know it, and I am not from Loongson, just some user trying to
mess around it.
There are some purposed "workarounds" like reducing the link speed (from
x16 to x8), tweaking the power management setting, etc.  Someone even
claims improving the heat sink of the LS7A chip can help to work around
this issue but I'm really skeptical...

Well when it's an ordering problem between writes and interrupts then nothing else than getting the order right will fix this. Otherwise it can always be that the CPU doesn't see coherent results from PCIe devices.

In other words if the CPU gets an interrupt but doesn't sees the fence value written it will assume the work is not done. But since the hardware won't trigger a second interrupt the CPU will then keep waiting for the operation to finish forever.

This is not limited to GPUs, but will potentially happen with network or disk I/O as well.


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