RE: [PATCH v1 0/4] [RFC] Implement Trampoline File Descriptor

David Laight
2020-07-29T08:36:41Z

From: Madhavan T. Venkataraman
> Sent: 28 July 2020 19:52
...
> trampfd faults are instruction faults that go through a different code path than
> the one that calls handle_mm_fault(). Perhaps, it is the handle_mm_fault() that
> is time consuming. Could you clarify?

Given that the expectation is a few instructions in userspace
(eg to pick up the original arguments for a nested call)
the (probable) thousands of clocks taken by entering the
kernel (especially with page table separation) is a massive
delta.

If entering the kernel were cheap no one would have added
the DSO functions for getting the time of day.

David

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