Re: [PATCH v4] eal: non-temporal memcpy

["Mattias Rönnblom" <hofors@lysator.liu.se>]

On 2023-07-31 14:25, Morten Brørup wrote:
>> From: Thomas Monjalon [mailto:thomas@monjalon.net]
>> Sent: Monday, 31 July 2023 14.14
>>
>> Hello,
>>
>> What's the status of this feature?
> 
> I haven't given up on upstreaming this feature, but there doesn't seem to be much demand for it, so working on it has low priority.
> 

This would definitely be a useful addition to the EAL, IMO.

It's also a case where it's difficult to provide a generic and portable 
solution with both good performance and reasonable semantics. The upside 
is you seem to come pretty far already.

>>
>>
>> 10/10/2022 08:46, Morten Brørup:
>>> This patch provides a function for memory copy using non-temporal store,
>>> load or both, controlled by flags passed to the function.
>>>
>>> Applications sometimes copy data to another memory location, which is only
>>> used much later.
>>> In this case, it is inefficient to pollute the data cache with the copied
>>> data.
>>>
>>> An example use case (originating from a real life application):
>>> Copying filtered packets, or the first part of them, into a capture buffer
>>> for offline analysis.
>>>
>>> The purpose of the function is to achieve a performance gain by not
>>> polluting the cache when copying data.
>>> Although the throughput can be improved by further optimization, I do not
>>> have time to do it now.
>>>
>>> The functional tests and performance tests for memory copy have been
>>> expanded to include non-temporal copying.
>>>
>>> A non-temporal version of the mbuf library's function to create a full
>>> copy of a given packet mbuf is provided.
>>>
>>> The packet capture and packet dump libraries have been updated to use
>>> non-temporal memory copy of the packets.
>>>
>>> Implementation notes:
>>>
>>> Implementations for non-x86 architectures can be provided by anyone at a
>>> later time. I am not going to do it.
>>>
>>> x86 non-temporal load instructions must be 16 byte aligned [1], and
>>> non-temporal store instructions must be 4, 8 or 16 byte aligned [2].
>>>
>>> ARM non-temporal load and store instructions seem to require 4 byte
>>> alignment [3].
>>>
>>> [1] https://www.intel.com/content/www/us/en/docs/intrinsics-guide/
>>> index.html#text=_mm_stream_load
>>> [2] https://www.intel.com/content/www/us/en/docs/intrinsics-guide/
>>> index.html#text=_mm_stream_si
>>> [3] https://developer.arm.com/documentation/100076/0100/
>>> A64-Instruction-Set-Reference/A64-Floating-point-Instructions/
>>> LDNP--SIMD-and-FP-
>>>
>>> This patch is a major rewrite from the RFC v3, so no version log comparing
>>> to the RFC is provided.
>>>
>>> v4
>>> * Also ignore the warning for clang int the workaround for
>>>    _mm_stream_load_si128() missing const in the parameter.
>>> * Add missing C linkage specifier in rte_memcpy.h.
>>>
>>> v3
>>> * _mm_stream_si64() is not supported on 32-bit x86 architecture, so only
>>>    use it on 64-bit x86 architecture.
>>> * CLANG warns that _mm_stream_load_si128_const() and
>>>    rte_memcpy_nt_15_or_less_s16a() are not public,
>>>    so remove __rte_internal from them. It also affects the documentation
>>>    for the functions, so the fix can't be limited to CLANG.
>>> * Use __rte_experimental instead of __rte_internal.
>>> * Replace <n> with nnn in function documentation; it doesn't look like
>>>    HTML.
>>> * Slightly modify the workaround for _mm_stream_load_si128() missing const
>>>    in the parameter; the ancient GCC 4.5.8 in RHEL7 doesn't understand
>>>    #pragma GCC diagnostic ignored "-Wdiscarded-qualifiers", so use
>>>    #pragma GCC diagnostic ignored "-Wcast-qual" instead. I hope that works.
>>> * Fixed one coding style issue missed in v2.
>>>
>>> v2
>>> * The last 16 byte block of data, incl. any trailing bytes, were not
>>>    copied from the source memory area in rte_memcpy_nt_buf().
>>> * Fix many coding style issues.
>>> * Add some missing header files.
>>> * Fix build time warning for non-x86 architectures by using a different
>>>    method to mark the flags parameter unused.
>>> * CLANG doesn't understand RTE_BUILD_BUG_ON(!__builtin_constant_p(flags)),
>>>    so omit it when using CLANG.
>>>
>>> Signed-off-by: Morten Brørup <mb@smartsharesystems.com>
>>> ---
>>>   app/test/test_memcpy.c               |   65 +-
>>>   app/test/test_memcpy_perf.c          |  187 ++--
>>>   lib/eal/include/generic/rte_memcpy.h |  127 +++
>>>   lib/eal/x86/include/rte_memcpy.h     | 1238 ++++++++++++++++++++++++++
>>>   lib/mbuf/rte_mbuf.c                  |   77 ++
>>>   lib/mbuf/rte_mbuf.h                  |   32 +
>>>   lib/mbuf/version.map                 |    1 +
>>>   lib/pcapng/rte_pcapng.c              |    3 +-
>>>   lib/pdump/rte_pdump.c                |    6 +-
>>>   9 files changed, 1645 insertions(+), 91 deletions(-)
>>
>>
>>
>