[dpdk-dev] dev Digest, Vol 159, Issue 119
pierre at emutex.com
Fri Sep 1 11:36:17 CEST 2017
This might not be a good idea. With these modifications, the functions
are not inlined any more (attribute inline), and not post-optimized
either (-f lto)
As per ABI, most of the registers must be saved on the stack before
invoking a function. This is not noticeable in isolated test/perf code
where there is not much context to save and restore at each function
call, but it destroys performance in real heavy application where it is
expected, for performance reasons, that rte_memcpy is really an inlined
leaf function and all code can be inlined and optimized at compile time.
The DPDK design logic has always been in the past to provide the most
efficient implementation for a designated target platform. Else there
would not be no advantage to provide rte_memcpy() over the standard
generic memcpy() function.
Such type of code is slowly starting to creep into DPDK codebase. an
other example is the support for dynamic callbacks in rte_eth_tx_burst().
If multi-platform MUST be supported at run time, the right trade-off
would be to make-sure this type of code can be compiled out, e.g. add
something like RTE_ENABLE_RUN_TIME_DISPATCH in the config file.
On 01/09/17 09:58, dev-request at dpdk.org wrote:
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> Today's Topics:
> 1. [PATCH v2 0/3] dynamic linking support (Xiaoyun Li)
> 2. [PATCH v2 1/3] eal/x86: run-time dispatch over memcpy (Xiaoyun Li)
> Message: 1
> Date: Fri, 1 Sep 2017 16:56:59 +0800
> From: Xiaoyun Li <xiaoyun.li at intel.com>
> To: bruce.richardson at intel.com
> Cc: dev at dpdk.org, zhihong.wang at intel.com, qi.z.zhang at intel.com,
> wenzhuo.lu at intel.com, Xiaoyun Li <xiaoyun.li at intel.com>
> Subject: [dpdk-dev] [PATCH v2 0/3] dynamic linking support
> Message-ID: <1504256222-32969-1-git-send-email-xiaoyun.li at intel.com>
> This patchset dynamically selects functions at run-time based on CPU flags
> that current machine supports. This patchset modifies mempcy, memcpy perf
> test and x86 EFD, using function pointers and bind them at constructor time.
> Then in the cloud environment, users can compiler once for the minimum target
> such as 'haswell'(not 'native') and run on different platforms (equal or above
> haswell) and can get ISA optimization based on running CPU.
> Xiaoyun Li (3):
> eal/x86: run-time dispatch over memcpy
> app/test: run-time dispatch over memcpy perf test
> efd: run-time dispatch over x86 EFD functions
> .../common/include/arch/x86/rte_memcpy.h | 343 +++++++++++++--------
> lib/librte_efd/rte_efd_x86.h | 41 ++-
> mk/rte.cpuflags.mk | 14 +
> test/test/test_memcpy_perf.c | 40 ++-
> 4 files changed, 296 insertions(+), 142 deletions(-)
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