Re: [PATCH] scsi: fc: force inlining of wwn conversion functions

[Chris Metcalf]

(Resending as text/plain)

On 4/27/2016 5:34 PM, Arnd Bergmann wrote:
> This won't help on TILE, which is the one architecture that sets
> ARCH_SUPPORTS_OPTIMIZED_INLINING but does not set ARCH_USE_BUILTIN_BSWAP.
> Chris Metcalf should be able to figure out whether we can just
> set ARCH_USE_BUILTIN_BSWAP for tile as well.

We certainly could enable ARCH_USE_BUILTIN_BSWAP.  The only problem is
that we never added explicit support for bswap16() in gcc, which is
efficiently done on tilegx via the "revbytes" instruction and a 48-bit
right-shift.  So gcc instead does a generic thing with four
instructions in three bundles, so really not as good as our asm/swab.h.

I'm not sure how to weigh the implications of converting to
builtin_bswap16 (and possibly upstreaming a better implementation to
gcc), vs. disabling ARCH_SUPPORTS_OPTIMIZED_INLINING (which no one
else but x86 uses anyway), vs. just ignoring the compiler bug and
hoping it's not an issue in practice :-)
--
Chris Metcalf, Mellanox Technologies
http://www.mellanox.com