From: Andy Chiu <andy.chiu@sifive.com>
To: palmer@dabbelt.com, paul.walmsley@sifive.com,
aou@eecs.berkeley.edu, rostedt@goodmis.org, mingo@redhat.com,
peterz@infradead.org, jpoimboe@kernel.org, jbaron@akamai.com,
ardb@kernel.org
Cc: greentime.hu@sifive.com, zong.li@sifive.com,
andy.chiu@sifive.com, guoren@kernel.org, kernel@esmil.dk,
linux-riscv@lists.infradead.org
Subject: [PATCH RFC v2 riscv/for-next 1/5] riscv: align ftrace to 4 Byte boundary and increase ftrace prologue size
Date: Tue, 13 Sep 2022 17:42:48 +0800 [thread overview]
Message-ID: <20220913094252.3555240-2-andy.chiu@sifive.com> (raw)
In-Reply-To: <20220913094252.3555240-1-andy.chiu@sifive.com>
We are introducing a new ftrace mechanism in order to phase out
stop_machine() and enable kernel preemption. The new mechanism requires
ftrace patchable function entries to be 24 bytes and aligned to 4 Byte
boundaries.
Before applying this patch, the size of the kernel code, with 122465 of
ftrace entries, was at 12.46 MB. Under the same configuration, the size
has increased to 12.99 MB after applying this patch set.
However, we found the -falign-functions alone was not strong enoungh to
make all functions align as required. In fact, cold functions are not
aligned after turning on optimizations. We consider this is a bug in GCC
and turn off guess-branch-probility as a workaround to align all
functions.
GCC bug id: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88345
Signed-off-by: Andy Chiu <andy.chiu@sifive.com>
Reviewed-by: Greentime Hu <greentime.hu@sifive.com>
---
arch/riscv/Makefile | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
index 3fa8ef336822..fd8069f59a59 100644
--- a/arch/riscv/Makefile
+++ b/arch/riscv/Makefile
@@ -11,7 +11,7 @@ LDFLAGS_vmlinux :=
ifeq ($(CONFIG_DYNAMIC_FTRACE),y)
LDFLAGS_vmlinux := --no-relax
KBUILD_CPPFLAGS += -DCC_USING_PATCHABLE_FUNCTION_ENTRY
- CC_FLAGS_FTRACE := -fpatchable-function-entry=8
+ CC_FLAGS_FTRACE := -fpatchable-function-entry=12 -falign-functions=4 -fno-guess-branch-probability
endif
ifeq ($(CONFIG_CMODEL_MEDLOW),y)
--
2.36.0
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next prev parent reply other threads:[~2022-09-13 9:44 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-13 9:42 [PATCH RFC v2 riscv/for-next 0/5] Enable ftrace with kernel preemption for RISC-V Andy Chiu
2022-09-13 9:42 ` Andy Chiu [this message]
2022-09-15 13:53 ` [PATCH RFC v2 riscv/for-next 1/5] riscv: align ftrace to 4 Byte boundary and increase ftrace prologue size Guo Ren
2022-09-17 1:15 ` Andy Chiu
2022-09-13 9:42 ` [PATCH RFC v2 riscv/for-next 2/5] riscv: export patch_insn_write Andy Chiu
2022-09-13 9:42 ` [PATCH RFC v2 riscv/for-next 3/5] riscv: ftrace: use indirect jump to work with kernel preemption Andy Chiu
2022-09-14 13:45 ` Guo Ren
2022-09-15 13:30 ` Guo Ren
2022-09-17 1:04 ` Andy Chiu
2022-09-17 10:56 ` Guo Ren
2024-02-20 14:17 ` Evgenii Shatokhin
2022-09-13 9:42 ` [PATCH RFC v2 riscv/for-next 4/5] riscv: ftrace: do not use stop_machine to update code Andy Chiu
2022-09-13 9:42 ` [PATCH RFC v2 riscv/for-next 5/5] riscv: align arch_static_branch function Andy Chiu
2022-09-14 14:06 ` Guo Ren
2022-09-16 23:54 ` Andy Chiu
2022-09-17 0:22 ` Guo Ren
2022-09-17 18:17 ` [PATCH] riscv: jump_label: Optimize size with RISCV_ISA_C guoren
2022-09-17 18:38 ` [PATCH RFC v2 riscv/for-next 5/5] riscv: align arch_static_branch function guoren
2022-09-17 23:49 ` Guo Ren
2022-09-17 23:59 ` Guo Ren
2022-09-18 0:12 ` Jessica Clarke
2022-09-18 0:46 ` Guo Ren
2022-09-14 14:24 ` Jessica Clarke
2022-09-15 1:47 ` Guo Ren
2022-09-15 2:34 ` Jessica Clarke
2024-02-13 19:42 ` [PATCH RFC v2 riscv/for-next 0/5] Enable ftrace with kernel preemption for RISC-V Evgenii Shatokhin
2024-02-21 5:27 ` Andy Chiu
2024-02-21 16:55 ` Evgenii Shatokhin
2024-03-06 20:57 ` Alexandre Ghiti
2024-03-07 8:35 ` Evgenii Shatokhin
2024-03-07 12:27 ` Andy Chiu
2024-03-07 13:21 ` Alexandre Ghiti
2024-03-07 15:57 ` Samuel Holland
2024-03-11 14:24 ` Andy Chiu
2024-03-19 14:50 ` Alexandre Ghiti
2024-03-19 14:58 ` Conor Dooley
2024-03-20 16:37 ` Andy Chiu
2024-03-18 15:31 ` Andy Chiu
2024-03-19 15:32 ` Evgenii Shatokhin
2024-03-20 16:38 ` Andy Chiu
2024-03-19 17:37 ` Alexandre Ghiti
2024-03-20 16:36 ` Andy Chiu
2024-03-21 11:02 ` Alexandre Ghiti
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