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From:   Michael Ellerman <mpe@ellerman.id.au>
To:     "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Christophe Leroy <christophe.leroy@csgroup.eu>,
        Ingo Molnar <mingo@redhat.com>,
        Paul Mackerras <paulus@samba.org>,
        Steven Rostedt <rostedt@goodmis.org>
Cc:     linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH v1 06/22] powerpc/ftrace: Inline ftrace_modify_code()
In-Reply-To: <1650261933.e8kr43zvw0.naveen@linux.ibm.com>
References: <cover.1648131740.git.christophe.leroy@csgroup.eu>
 <3b651381f4c53988ede62f4a1505e7e8ccab56b4.1648131740.git.christophe.leroy@csgroup.eu>
 <1650261933.e8kr43zvw0.naveen@linux.ibm.com>
Date:   Fri, 22 Apr 2022 19:12:44 +1000
Message-ID: <87wnfh8os3.fsf@mpe.ellerman.id.au>
MIME-Version: 1.0
Content-Type: text/plain
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"Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> writes:
> Christophe Leroy wrote:
>> Inlining ftrace_modify_code(), it increases a bit the
>> size of ftrace code but brings 5% improvment on ftrace
>> activation.
>> 
>> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
>> ---
>>  arch/powerpc/kernel/trace/ftrace.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>> diff --git a/arch/powerpc/kernel/trace/ftrace.c b/arch/powerpc/kernel/trace/ftrace.c
>> index 41c45b9c7f39..98e82fa4980f 100644
>> --- a/arch/powerpc/kernel/trace/ftrace.c
>> +++ b/arch/powerpc/kernel/trace/ftrace.c
>> @@ -53,7 +53,7 @@ ftrace_call_replace(unsigned long ip, unsigned long addr, int link)
>>  	return op;
>>  }
>> 
>> -static int
>> +static inline int
>>  ftrace_modify_code(unsigned long ip, ppc_inst_t old, ppc_inst_t new)
>>  {
>>  	ppc_inst_t replaced;
>
> I thought gcc was free to inline functions without the need for 
> 'inline'.

Yes it is.

> On the flip side, don't we need __always_inline if we want to force 
> inlining?

Yes. Since ac7c3e4ff401 ("compiler: enable CONFIG_OPTIMIZE_INLINING forcibly").

cheers