config: add option for atomic mbuf reference counting

RTE_MBUF_REFCNT_ATOMIC = 0 is not necessary for applications like
Seastar, where it's safe to assume that the mbuf refcnt is only
updated by a single core only.

Signed-off-by: Kefu Chai <tchaikov@gmail.com>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>

config/meson.build

@@ -299,7 +299,9 @@ if dpdk_conf.get('RTE_ARCH_64')
 else # for 32-bit we need smaller reserved memory areas
     dpdk_conf.set('RTE_MAX_MEM_MB', 2048)
 endif
-
+if get_option('mbuf_refcnt_atomic')
+    dpdk_conf.set('RTE_MBUF_REFCNT_ATOMIC', true)
+endif
 
 compile_time_cpuflags = []
 subdir(arch_subdir)

config/rte_config.h

@@ -50,7 +50,6 @@
 
 /* mbuf defines */
 #define RTE_MBUF_DEFAULT_MEMPOOL_OPS "ring_mp_mc"
-#define RTE_MBUF_REFCNT_ATOMIC 1
 #define RTE_PKTMBUF_HEADROOM 128
 
 /* ether defines */

meson_options.txt

@@ -38,6 +38,8 @@ option('max_lcores', type: 'string', value: 'default', description:
        'Set maximum number of cores/threads supported by EAL; "default" is different per-arch, "detect" detects the number of cores on the build machine.')
 option('max_numa_nodes', type: 'string', value: 'default', description:
        'Set the highest NUMA node supported by EAL; "default" is different per-arch, "detect" detects the highest NUMA node on the build machine.')
+option('mbuf_refcnt_atomic', type: 'boolean', value: true, description:
+       'Atomically access the mbuf refcnt.')
 option('platform', type: 'string', value: 'native', description:
        'Platform to build, either "native", "generic" or a SoC. Please refer to the Linux build guide for more information.')
 option('enable_trace_fp', type: 'boolean', value: false, description: