On 2022-08-10 23:20, Honnappa Nagarahalli wrote:
<snip>
From: Mattias Rönnblom [mailto:hof...@lysator.liu.se]
Sent: Wednesday, 10 August 2022 13.56
On 2022-08-09 17:26, Stephen Hemminger wrote:
[...]
Alignment seems like a non-issue to me. A NT-store memcpy() can be
made free of alignment requirements, incurring only a very slight cost
for the always-aligned case (who has their data always 16-byte aligned
anyways?).
The memory barrier required on x86 seems like a bigger issue.
Maybe rte_non_cache_copy()?
rte_memcpy_nt_weakly_ordered(), or rte_memcpy_nt_weak(). And a
rte_memcpy_nt() with the sfence is place, which the user hopefully
will find first? I don't know. I would prefer not having the weak
variant at all.
I think providing weakly ordered version is required to offset the cost of the
barriers. One might be able to copy multiple packets and then issue a barrier.
On what architecture?
I assumed that only x86 had the peculiar property of having different
memory models for regular and NT load/stores.
Accepting weak memory ordering (i.e., no sfence) could also be one of
the flags, assuming rte_memcpy_nt() would have a flags parameter.
Default is safe (=memcpy() semantics), but potentially slower.
Excellent idea!
Want to avoid the naive user just doing s/memcpy/rte_memcpy_nt/ and
expect
everything to work.
