From: Sachin Saxena <sachin.saxena@nxp.com>
To: Marvin Liu <yong.liu@intel.com>,
"zhiyong.yang@intel.com" <zhiyong.yang@intel.com>,
"thomas@monjalon.net" <thomas@monjalon.net>,
"dev@dpdk.org" <dev@dpdk.org>
Subject: Re: [dpdk-dev] [PATCH] mk: using initial-exec model for thread local variable
Date: Thu, 5 Jul 2018 14:46:24 +0000 [thread overview]
Message-ID: <HE1PR0401MB1772274CE71E8959117A22B4E3400@HE1PR0401MB1772.eurprd04.prod.outlook.com> (raw)
In-Reply-To: <20180705141321.129989-1-yong.liu@intel.com>
>
> 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.liu@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
next prev parent reply other threads:[~2018-07-05 14:46 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-05 14:13 Marvin Liu
2018-07-05 9:25 ` Thomas Monjalon
2018-07-05 14:46 ` Sachin Saxena [this message]
2018-07-06 2:22 ` Liu, Yong
2018-07-06 10:02 ` Bruce Richardson
-- strict thread matches above, loose matches on Subject: below --
2018-04-28 9:54 Marvin Liu
2018-04-28 4:39 ` Yang, Zhiyong
2018-05-18 9:46 ` Thomas Monjalon
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=HE1PR0401MB1772274CE71E8959117A22B4E3400@HE1PR0401MB1772.eurprd04.prod.outlook.com \
--to=sachin.saxena@nxp.com \
--cc=dev@dpdk.org \
--cc=thomas@monjalon.net \
--cc=yong.liu@intel.com \
--cc=zhiyong.yang@intel.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).