That was already suggested to Jerome, see his first email in this thread. — Damjan
> On 18.07.2021., at 16:05, Andrew Yourtchenko <ayour...@gmail.com> wrote: > > Naive question: if someone needs a lot of space to prepend in front of the > buffer, would it make sense to allocate an entire new buffer and place it as > the very first one in the chain ? That would save a recompile and also me > more generic and extensible (you can get 2,3,4,… buffers in the same fashion > then?) I don’t know if we have the easy facility to do this in VPP, though. > > This would avoid a recompile and would work on the wider range of setups, if > it were possible… > > --a > >>> On 17 Jul 2021, at 16:58, jerome.bay...@student.uliege.be wrote: >>> >> >> Hello Benoit, >> >> Thank you for your answer about buffer allocation in batches, my solution is >> way more efficient now. >> >> However, I still want to try to change the value of the "PRE_DATA_SIZE" >> cmake variable to see how it behaves with a greater value (i.e 256 instead >> of 128). To do so, I followed the method given in the documentation at the >> following url : >> https://fd.io/docs/vpp/master/gettingstarted/developers/buildsystem/cmakeandninja.html#tinkering-with-build-options-ccmake. >> The issue is that once I've changed the value of the "PRE_DATA_SIZE" >> variable, I press "c" to regenerate files that need to be regenerated and >> then I get this error in cmake output : >> >> CMake Error at cmake/misc.cmake:27 (_message): >> [1;31mDPDK RTE_PKTMBUF_HEADROOM (128) ;must be equal to PRE_DATA_SIZE >> (256)[m >> Call Stack (most recent call first): >> plugins/dpdk/CMakeLists.txt:65 (message) >> >> I guess I should also modify the value of "DPDK RTE_PKTMBUF_HEADROOM" but I >> don't know how I can do it ? Indeed, I can't find where this variable is >> defined. >> >> Jérôme >> >> De: "Benoit Ganne (bganne)" <bga...@cisco.com> >> À: "jerome bayaux" <jerome.bay...@student.uliege.be>, vpp-dev@lists.fd.io >> Cc: "Justin Iurman" <justin.iur...@uliege.be> >> Envoyé: Jeudi 15 Juillet 2021 19:16:32 >> Objet: RE: Buffer chains and pre-data area >> >> Hi Jerome, >> >> > However, when I tried to perform some performance tests I was quite >> > disappointed by the results : the buffer allocation for each packet is not >> > efficient at all. My question is then : Is there any way to increase the >> > performances ? To allocate buffers, I use the function "vlib_buffer_alloc" >> > defined in "buffer_funcs.h" but is it the right function to use ? >> >> Do you allocate buffers in batch? Let's say you want to encapsulate a batch >> of packets, instead of doing: >> >> while (n_left) >> u32 bi >> vlib_buffer_t *b >> vlib_buffer_alloc(vm, &bi, 1) >> b = vlib_get_buffer (vm, bi) >> add b to the chain >> ... >> >> You should do something like (allocation error checking etc. is left as an >> exercise): >> >> u32 bi[VLIB_FRAME_SIZE] >> vlib_buffer_t *bufs[VLIB_FRAME_SIZE] >> vlib_buffer_alloc (vm, bi, n_left) >> vlib_get_buffers (vm, bi, bufs, n_left) >> >> while (n_left) >> add bufs[i] to the chain >> ... >> >> > In my case, the best option would be to have more space available in the >> > buffer's pre-data area but VPP does not seem to be built in a way that >> > allows easy modifications of the "PRE_DATA_SIZE" value. Am I right or is >> > there any "clean" method to change this value ? >> >> It is define as a cmake variable and can be customize through eg. cmake-gui. >> >> ben >> >> >> >> > > >
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