NAT: VPP-1531 api cleanup & update - vpp - Vector Packet Processing

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author	Filip Varga <fivarga@cisco.com>	2019-04-15 18:52:43 +0200
committer	Ole Trøan <otroan@employees.org>	2019-04-24 11:09:37 +0000
commit	dd1e3e780cd480e3f29fc34df48e605ded1acb2c (patch)
tree	29ecae4a0f965a65b96886ee06438adeb6a14d21 /test/vpp_pg_interface.py
parent	58c7580b1641879c91ac708162f1c3fccbb67302 (diff)

NAT: VPP-1531 api cleanup & update

Change-Id: I2492400a67b39a3adbc24ab7cf1ba17a409e95a8 Signed-off-by: Filip Varga <fivarga@cisco.com>

Diffstat (limited to 'test/vpp_pg_interface.py')

0 files changed, 0 insertions, 0 deletions

Multi-Architecture Graph Node Cookbook ====================================== In the context of graph node dispatch functions, it's easy enough to use the vpp multi-architecture support setup. The point of the scheme is simple: for performance-critical nodes, generate multiple CPU hardware-dependent versions of the node dispatch functions, and pick the best one at runtime. The vpp scheme is simple enough to use, but details matter. 100,000 foot view ----------------- We compile entire graph node dispatch function implementation files multiple times. These compilations give rise to multiple versions of the graph node dispatch functions. Per-node constructor-functions interrogate CPU hardware, select the node dispatch function variant to use, and set the vlib_node_registration_t ".function" member to the address of the selected variant. Details ------- Declare the node dispatch function as shown, using the VLIB\_NODE\_FN macro. The name of the node function **MUST** match the name of the graph node. :: VLIB_NODE_FN (ip4_sdp_node) (vlib_main_t * vm, vlib_node_runtime_t * node, vlib_frame_t * frame) { if (PREDICT_FALSE (node->flags & VLIB_NODE_FLAG_TRACE)) return ip46_sdp_inline (vm, node, frame, 1 /* is_ip4 */ , 1 /* is_trace */ ); else return ip46_sdp_inline (vm, node, frame, 1 /* is_ip4 */ , 0 /* is_trace */ ); } We need to generate *precisely one copy* of the vlib_node_registration_t, error strings, and packet trace decode function. Simply bracket these items with "#ifndef CLIB_MARCH_VARIANT...#endif": :: #ifndef CLIB_MARCH_VARIANT static u8 * format_sdp_trace (u8 * s, va_list * args) { <snip> } #endif ... #ifndef CLIB_MARCH_VARIANT static char *sdp_error_strings[] = { #define _(sym,string) string, foreach_sdp_error #undef _ }; #endif ... #ifndef CLIB_MARCH_VARIANT VLIB_REGISTER_NODE (ip4_sdp_node) = { // DO NOT set the .function structure member. // The multiarch selection __attribute__((constructor)) function // takes care of it at runtime .name = "ip4-sdp", .vector_size = sizeof (u32), .format_trace = format_sdp_trace, .type = VLIB_NODE_TYPE_INTERNAL, .n_errors = ARRAY_LEN(sdp_error_strings), .error_strings = sdp_error_strings, .n_next_nodes = SDP_N_NEXT, /* edit / add dispositions here */ .next_nodes = { [SDP_NEXT_DROP] = "ip4-drop", }, }; #endif To belabor the point: *do not* set the ".function" member! That's the job of the multi-arch selection \_\_attribute\_\_((constructor)) function Always inline node dispatch functions ------------------------------------- It's typical for a graph dispatch function to contain one or more calls to an inline function. See above. If your node dispatch function is structured that way, make *ABSOLUTELY CERTAIN* to use the "always_inline" macro: :: always_inline uword ip46_sdp_inline (vlib_main_t * vm, vlib_node_runtime_t * node, vlib_frame_t * frame, int is_ip4, int is_trace) { ... } Otherwise, the compiler is highly likely NOT to build multiple versions of the guts of your dispatch function. It's fairly easy to spot this mistake in "perf top." If you see, for example, a bunch of functions with names of the form "xxx_node_fn_avx2" in the profile, *BUT* your brand-new node function shows up with a name of the form "xxx_inline.isra.1", it's quite likely that the inline was declared "static inline" instead of "always_inline". Add the required Makefile.am content ------------------------------------ If the component in question already sets a "multiversioning_sources" variable, simply add the indicated .c file to the list. If not, add the required boilerplate: :: if CPU_X86_64 sdp_multiversioning_sources = \ sdp/node.c \ sdp/sdp_slookup.c if CC_SUPPORTS_AVX2 ############################################################### # AVX2 ############################################################### libsdp_plugin_avx2_la_SOURCES = $(sdp_multiversioning_sources) libsdp_plugin_avx2_la_CFLAGS = \ $(AM_CFLAGS) @CPU_AVX2_FLAGS@ \ -DCLIB_MARCH_VARIANT=avx2 noinst_LTLIBRARIES += libsdp_plugin_avx2.la sdp_plugin_la_LIBADD += libsdp_plugin_avx2.la endif if CC_SUPPORTS_AVX512 ############################################################### # AVX512 ############################################################### libsdp_plugin_avx512_la_SOURCES = $(sdp_multiversioning_sources) libsdp_plugin_avx512_la_CFLAGS = \ $(AM_CFLAGS) @CPU_AVX512_FLAGS@ \ -DCLIB_MARCH_VARIANT=avx512 noinst_LTLIBRARIES += libsdp_plugin_avx512.la sdp_plugin_la_LIBADD += libsdp_plugin_avx512.la endif endif A certain amount of cut-paste-modify is currently required. Hopefully we'll manage to improve the scheme in the future.


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