Instructions cache flush on ARM (was: N800 Video playback)
On Friday 20 April 2007 19:04, you wrote:
I have seen your code in xserver which does the same job for downscaling,
but in nonoptimized C and with much higher impact on quality. Using JIT
scaler there can improve both image quality and performance a lot. The
only my concern is about instruction cache coherency. As ARM requires
explicit instructions cache flush for self modyfying or dynamically
generated code, I wonder if using just mmap is safe (does it flush cache
for allocated region of memory?). Maybe maemo kernel hackers/developers
can help with this information?
arm linux support flush icache by syscall cacheflush,
qemu have this function:
static inline void flush_icache_range(unsigned long start, unsigned long
stop)
{
register unsigned long _beg __asm (a1) = start;
register unsigned long _end __asm (a2) = stop;
register unsigned long _flg __asm (a3) = 0;
__asm __volatile__ (swi 0x9f0002 : : r (_beg), r (_end), r
(_flg));
}
you can reference kernel source arch/arm/kernel/traps.c and
include/asm-arm/unistd.h
Thanks, it works. But I'm worried about [1]. Looks like EABI has a new syscall
interface and this code from qemu uses old ABI. And from reading description
at the wiki page, compatibility with old ABI can be disabled (and it makes
sense disabling it as this compatibility reduces performance a bit).
I wonder if there is a better portable solution (running on any ARM linux or
even better on any POSIX compatible system). It would be reasonable to
assume that allocating memory with mmap implies that we are going to
execute code from that area and instructions cache should be flushed for it:
mmap(0, some_buffer_size, PROT_READ | PROT_WRITE | PROT_EXEC,
MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
But I wonder if mmap requesting executable block of memory really does
instructions cache flush in reality?
I just want to submit this ARM optimized scaler to upstream ffmpeg and want to
make it as portable as possible.
1.
http://wiki.debian.org/ArmEabiPort#head-96054c6cb4209b4a589e645dd50ac0fe133b8ced
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Re: IT2007 Hacker Edition - First impression: Onscreen keyboard
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Re: Compiling latest kernel (from kernel.org) in n800
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Re: trouble to disconnect from WiFi AP
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