On ARM platforms, accessing the PMU registers requires special user
access permissions. Since there is no other way to get accurate timers,
the current implementation of timers in FFmpeg rely on these registers.
Unfortunately, enabling user access to these registers on Linux is not
trivial, and generally involve compiling a random and unreliable github
kernel module, or patching somehow your kernel.
Such module is very unlikely to reach the upstream anytime soon. Quoting
Robin Murphin from ARM:
> Say you do give userspace direct access to the PMU; now run two or more
> programs at once that believe they can use the counters for their own
> "minimal-overhead" profiling. Have fun interpreting those results...
>
> And that's not even getting into the implications of scheduling across
> different CPUs, CPUidle, etc. where the PMU state is completely beyond
> userspace's control. In general, the plan to provide userspace with
> something which might happen to just about work in a few corner cases,
> but is meaningless, misleading or downright broken in all others, is to
> never do so.
As a result, the alternative is to use the Performance Monitoring Linux
API which makes use of these registers internally (assuming the PMU of
your ARM board is supported in the kernel, which is definitely not a
given...).
While the Linux API is obviously cross platform, it does have a
significant overhead which needs to be taken into account. As a result,
that mode is only weakly enabled on ARM platforms exclusively.
Note on the non flexibility of the implementation: the timers (native
FFmpeg vs Linux API) are selected at compilation time to prevent the
need of function calls, which would result in a negative impact on the
cycle counters.
Meant for DSP functions returning a float or double, as they'd fail if emms
is called after every run on x86_32.
Signed-off-by: James Almer <jamrial@gmail.com>
* commit 'c91d6a33f872574c95c8784277cf60ffcf6bff4f':
checkasm: aarch64: Add filler args to make sure all parameters are passed on the stack
Merged-by: James Almer <jamrial@gmail.com>
* commit 'f1b3e131385176c3c9d9783b25047856a0dcebf6':
checkasm: aarch64: Clobber the stack before calling functions
Merged-by: James Almer <jamrial@gmail.com>
* commit '22c3ab18646924ce24dc6017a9e882ff69689e40':
checkasm: Add test for huffyuvdsp add_bytes
huffyuvdsp is renamed to llviddsp to be consistent with our codebase.
Note: af607b7e07 wasn't actually required for this test since this
commit is not actually testing huffyuvdsp.
Merged-by: Clément Bœsch <u@pkh.me>
This, combined with clobbering the stack space prior to the call,
increases the chances of finding cases where 32 bit parameters
are erroneously treated as 64 bit.
Signed-off-by: Martin Storsjö <martin@martin.st>
The functions may not clean up properly after using MMX
registers. For the normal testing calls, the checkasm_checked_call
functions will do the cleanup (and check that functions that
should clean up do it as well), but when benchmarking functions
that don't clean up, we don't currently properly clean up at all.
This causes issues if a benchmarked function is followed by testing
of a function that is supposed to not clobber the MMX/FPU state but
doesn't touch it at all.
Signed-off-by: Martin Storsjö <martin@martin.st>
