[dm-devel] [patch 4/4] dm-writecache: use new API for flushing

[Jeff Moyer]

Dan Williams <dan.j.williams at intel.com> writes:

> When I read your patch I came away with the impression that ARM had
> not added memcpy_flushcache() yet and you were working around that
> fact. Now that I look, ARM *does* define memcpy_flushcache() and
> you're avoiding it. You use memcpy+arch_wb_pmem where arch_wb_pmem on
> ARM64 is defined as __clean_dcache_area_pop(dst, cnt). The ARM
> memcpy_flushcache() implementation is:
>
>     memcpy(dst, src, cnt);
>     __clean_dcache_area_pop(dst, cnt);
>
> So, I do not see how what you're doing is any less work unless you are
> flushing less than you copy?
>
> If memcpy_flushcache() is slower than memcpy + arch_wb_pmem then the
> ARM implementation is broken and that needs to be addressed not worked
> around in a driver.

I think Mikulas wanted to batch up multiple copies and flush at the
end.  According to his commit message, that batching gained him 2%
performance.

-Jeff