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

[Jeff Moyer]

Jeff Moyer <jmoyer at redhat.com> writes:

> 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.

Nevermind me, I just caught up with the rest of the thread.  :)

-Jeff