linux-kernel - [PATCH v1 4/4] powerpc/code-patching: Use jump_label to check if poking

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Date:   Tue, 22 Mar 2022 16:40:21 +0100
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     Christophe Leroy <christophe.leroy@...roup.eu>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH v1 4/4] powerpc/code-patching: Use jump_label to check if poking_init() is done

It's only during early startup that poking_init() is not done yet,
for instance when calling ftrace_init().

Once poking_init() has been called there must be a poking area, no
need to check it everytime patch_instruction() is called.

ftrace activation time is reduced by 7% with the change on an 8xx.

Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
 arch/powerpc/lib/code-patching.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c
index ab434c3853c9..8bd74bbe8b8d 100644
--- a/arch/powerpc/lib/code-patching.c
+++ b/arch/powerpc/lib/code-patching.c
@@ -79,6 +79,8 @@ static int text_area_cpu_down(unsigned int cpu)
 	return 0;
 }
 
+static __ro_after_init DEFINE_STATIC_KEY_FALSE(poking_init_done);
+
 /*
  * Although BUG_ON() is rude, in this case it should only happen if ENOMEM, and
  * we judge it as being preferable to a kernel that will crash later when
@@ -89,6 +91,7 @@ void __init poking_init(void)
 	BUG_ON(!cpuhp_setup_state(CPUHP_AP_ONLINE_DYN,
 		"powerpc/text_poke:online", text_area_cpu_up,
 		text_area_cpu_down));
+	static_branch_enable(&poking_init_done);
 }
 
 static unsigned long get_patch_pfn(void *addr)
@@ -176,7 +179,7 @@ static int do_patch_instruction(u32 *addr, ppc_inst_t instr)
 	 * when text_poke_area is not ready, but we still need
 	 * to allow patching. We just do the plain old patching
 	 */
-	if (!this_cpu_read(text_poke_area))
+	if (!static_branch_likely(&poking_init_done))
 		return raw_patch_instruction(addr, instr);
 
 	local_irq_save(flags);
-- 
2.35.1