>
> When building share library, thread-local storage model will be changed to
> global-dynamic. It will add additional cost for reading thread local variable.
> On the other hand, dynamically load share library with static TLS will request
> additional DTV slot which is limited by loader. By now only librte_pmd_eal.so
> contain thread local variable. So that can make TLS model back to initial-exec
> like static library for better performance.
>
> Signed-off-by: Marvin Liu <yong....@intel.com>
>
> diff --git a/mk/toolchain/gcc/rte.vars.mk b/mk/toolchain/gcc/rte.vars.mk
> index 7e4531bab..19d5e11ef 100644
> --- a/mk/toolchain/gcc/rte.vars.mk
> +++ b/mk/toolchain/gcc/rte.vars.mk
> @@ -43,6 +43,13 @@ ifeq (,$(findstring -O0,$(EXTRA_CFLAGS))) endif endif
>
> +# Initial execution TLS model has better performane compared to dynamic
> +# global. But this model require for addtional slot on DTV when dlopen
> +# object with thread local variable.
> +ifeq ($(CONFIG_RTE_BUILD_SHARED_LIB),y)
> +TOOLCHAIN_CFLAGS += -ftls-model=initial-exec endif
> +
[Sachin Saxena] Using initial-exec model for shared object is not
recommended. If you link a shared object containing IE-model, the object will
have the DF_STATIC_TLS flag set. By the spec, this means that dlopen() might
refuse to load it if TLS usage is greater than static TLS space.
This is what happening, when I tried to validate this change on ARM64 based NXP
platform with VPP-dpdk solution. VPP initialization fails with following error:
"load_one_plugin:145: /usr/lib/vpp_plugins/dpdk_plugin.so: cannot allocate
memory in static TLS block"
Note that dpdk dpaa2 driver and VPP both uses TLS variables quite
significantly. When forced to Initial-exec model in dpdk shared object, VPP
static TLS space is getting exhausted and dlopen() returns error while trying
to load the DPDK object.
For same reason, when we use "-fPIC" the default TLS model changed to
"global-dynamics" from "Initial-exec".
In my opinion, this change should not be merged as it is breaking basic
functionality.
> WERROR_FLAGS := -W -Wall -Wstrict-prototypes -Wmissing-prototypes
> WERROR_FLAGS += -Wmissing-declarations -Wold-style-definition -Wpointer-
> arith WERROR_FLAGS += -Wcast-align -Wnested-externs -Wcast-qual
> --
> 2.17.0
