On 26 July 2013 20:58, Wolfgang Denk wd@denx.de wrote:
Dear Andy Green,
In message 20130726065323.27333.82421.stgit@localhost.localdomain you wrote:
While studying the reason why kernel copy from NOR was so slow on our platform, I realized U-Boot is pulling it from 32-bit NOR in 8-bit chunks needlessly.
bootm uses memmove() and that just takes the approach by default to move u8s around.
This optimization prefers memcpy() implementation (done mostly in 32-bit reads and writes) if there's no overlap in source and dest, resulting in a huge speedup on our platform (480ms copy from 32-bit NOR ---> 140ms)
Sorry, but I dislike your patch.
I see.
Instead of making assumptions on the performance of memcpy() and
As I wrote, I measured the performance and got a very big gain, it's > 3x faster on my setup to use memcpy() then default memmove().
By calling that an "assumption" you're saying that there exist platforms where 32-bit linear memmove() is slower than doing it with 8-bit actions?
adding the overhead of an additional function call (which can be expensive especially for short copy operations) it would make more
I am not sure U-Boot is really in the business of doing small memmoves, but okay...
sense to pull the "copy a word at a time" code from memcpy() into memmove(), too.
On the other hand - if you really care about performance, then why do
I spent several hours figuring out why our NOR boot performance was terrible.... it's because this default memmove code is gloriously inefficient for all cases.
If you like it like that, no worries.
you not make sure that you provide optimized implementations for such functions and consequently #define __HAVE_ARCH_MEMMOVE (and __HAVE_ARCH_MEMCPY) ?
Yes I found these afterwards... performance is slightly better than memcpy() thanks to Nicolas Pitre it seems. The U-Boot config for the platform we have didn't know about them, it's much better with them.
After I wrote this patch it was also pointed out by Will Newton at Linaro that we have Neon accelerated memcpy lying around with BSD license....
https://launchpad.net/cortex-strings
however for my purposes NOR boot is working good enough with the ARCH versions.
-Andy
Best regards,
Wolfgang Denk
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