From: Josh Poimboeuf <jpoimboe@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>,
x86@kernel.org, linux-kernel@vger.kernel.org,
Josh Poimboeuf <jpoimboe@redhat.com>,
christophe.leroy@csgroup.eu, naveen.n.rao@linux.vnet.ibm.com,
mbenes@suse.cz
Subject: Re: [RFC][PATCH] ftrace,objtool: PC32 based __mcount_loc
Date: Fri, 17 Jun 2022 13:11:42 -0700 [thread overview]
Message-ID: <20220617201142.yea5ze7od43fat4o@treble> (raw)
In-Reply-To: <YqxkhV1YcI6e+xXp@worktop.programming.kicks-ass.net>
On Fri, Jun 17, 2022 at 01:24:53PM +0200, Peter Zijlstra wrote:
>
> Hi,
>
> I recently noticed that __mcount_loc is 64bit wide, containing absolute
> addresses. Since __mcount_loc is a permanent section (not one we drop
> after boot), this bloats the kernel memory usage for no real purpose.
>
> The below patch adds __mcount_loc_32 and objtool support to generate it.
> This saves, on an x86_64-defconfig + FTRACE, 23975*4 ~= 94K of permanent
> storage.
>
> XXX hobbled sorttable for now
> XXX compile tested only
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Nice!
Some nits:
- No need for renaming the section, it can still be called
'__mcount_loc' regardless?
- No need for a new FTRACE_MCOUNT32_USE_OBJTOOL config option or
'--mcount32' cmdline option, just change the old ones to be pc32?
- change "32" to "PC32": CC_USING_MCOUNT_LOC_PC32
That will shrink this patch down quite a bit.
--
Josh
next prev parent reply other threads:[~2022-06-17 20:11 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-17 11:24 [RFC][PATCH] ftrace,objtool: PC32 based __mcount_loc Peter Zijlstra
2022-06-17 11:40 ` Mark Rutland
2022-06-21 16:27 ` Ard Biesheuvel
2022-06-23 14:19 ` Mark Rutland
2022-06-22 14:54 ` Steven Rostedt
2022-06-23 14:21 ` Mark Rutland
2022-06-24 0:01 ` Steven Rostedt
2022-06-17 11:44 ` Christophe Leroy
2022-06-17 12:06 ` Peter Zijlstra
2022-06-17 20:11 ` Josh Poimboeuf [this message]
2022-06-20 7:35 ` Peter Zijlstra
2022-06-20 7:42 ` Christophe Leroy
2022-06-22 14:50 ` Steven Rostedt
2022-06-24 7:16 ` Peter Zijlstra
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