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
|
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)"
À: "jerome bayaux" , vpp-dev@lists.fd.io
Cc: "Justin Iurman"
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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