Hi,
We have a packaging/linking/optimization problem at LNG, I hope you guys
can give us some advice on that. (Cc'ing ODP list in case someone want
to add something)
We have OpenDataPlane (ODP), an API stretching between userspace
applications and hardware SDKs. It's defined in the form of C headers,
and we already have several implementations to face SDKs (or whathever
is actually controlling the hardware), e.g. linux-generic, a DPDK one etc.
And we have applications, like Open vSwitch (OVS), which now is able to
work with any ODP platform implementation which implements this API
When it comes to packaging, the ideal scenario would be to create one
package for the application, e.g. openvswitch.deb, and one for each
platform, e.g odp-generic.deb, odp-dpdk.deb. The latter would contain
the implementations in the form of a libodp.so file, so the application
can dynamically load the actually installed platform's library runtime,
with all the benefits of dynamic linking.
The trouble is that we have several accessor functions in the API which
are very short and __very__ frequently used. The best example is
"uint32_t odp_packet_len(odp_packet_t pkt)", which returns the length of
the packet. odp_packet_t is an opaque type defined by the
implementation, often a pointer to the packet's actual metadata, so the
actual function call yields to a simple load from that metadata pointer
(+offset). Having it wrapped into a function call brings a significant
performance decrease: when forwarding 64 byte packets at 10 Gbps, I got
13.2 Mpps with function calls. When I've inlined that function it
brought 13.8 Mpps, that's ~5% difference. And there are a lot of other
frequently used short accessor functions with the same problem.
But obviously if I inline these functions I break the ABI, and I need to
compile the application for each platform (and create packages like
openvswitch-odp-dpdk.deb, containing the platform statically linked).
I've tried to look around on Google and in gcc manual, but I couldn't
find a good solution for this kind of problem.
I've checked link time optimization (-flto), but it only helps with
static linking. Is there any way to keep the ODP application and
platform implementation binaries in separate files while having the
performance benefit of inlining?
Regards,
Zoltan
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