From: Andy Lutomirski <luto@amacapital.net>
To: Brian Gerst <brgerst@gmail.com>
Cc: Borislav Petkov <bp@suse.de>,
"the arch/x86 maintainers" <x86@kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
Denys Vlasenko <dvlasenk@redhat.com>,
Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH] x86: static_cpu_has_safe: discard dynamic check after init
Date: Mon, 18 Jan 2016 09:49:31 -0800 [thread overview]
Message-ID: <CALCETrUOiN92SjeNJjNeY+=QWk84EBWF6xS6nv6JL+tL5CKBCQ@mail.gmail.com> (raw)
In-Reply-To: <CAMzpN2i+LELbLaBbxDS0MF1Y0sn_Jm3ztCWATzMyrp4rnhWRQA@mail.gmail.com>
On Mon, Jan 18, 2016 at 8:52 AM, Brian Gerst <brgerst@gmail.com> wrote:
> On Sun, Jan 17, 2016 at 5:33 AM, Borislav Petkov <bp@suse.de> wrote:
>> On Sat, Jan 16, 2016 at 02:58:21PM -0500, Brian Gerst wrote:
>>> It saves space. The only thing left in main text is one jump
>>> instruction (5 bytes).
>>
>> How do I measure this?
>>
>> Because with my tailored config here, the only thing I'm seeing is a growth of
>> text by 730 bytes:
>>
>> before:
>> text data bss dec hex filename
>> 10926552 3598944 16642048 31167544 1db9438 vmlinux
>>
>> [ 0.056552] Freeing SMP alternatives memory: 24K (ffffffff81dd7000 - ffffffff81ddd000)
>> [ 2.883728] Freeing unused kernel memory: 2904K (ffffffff81b01000 - ffffffff81dd7000)
>>
>>
>> after:
>> text data bss dec hex filename
>> 10927282 3598944 16642048 31168274 1db9712 vmlinux
>>
>> [ 0.052559] Freeing SMP alternatives memory: 24K (ffffffff81dd7000 - ffffffff81ddd000)
>> [ 3.225318] Freeing unused kernel memory: 2904K (ffffffff81b01000 - ffffffff81dd7000)
>
> It is due to page alignment padding. It was not enough to lose a
> whole page from .text in your case.
>
> The size command includes any section that is marked executable in the
> text count, including init text. If you use readelf -S vmlinux.o
> instead you will notice that .text is the same size or smaller, and
> .static_cpu_has (which is freed after boot) is the difference.
>
If I'm understanding this correctly, the total non-init overhead from
static_cpu_has_safe with your patch is five bytes. I'd imagine that
the short jmp optimization in regular static_cpu_has essentially never
works, which means it will also use five bytes of text, which makes me
wonder whether we should just make static_cpu_has safe and remove the
distinction.
Also, someone should write a little script to measure kernel size
minus .init stuff.
--Andy
next prev parent reply other threads:[~2016-01-18 17:49 UTC|newest]
Thread overview: 66+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-16 19:22 [PATCH] x86: static_cpu_has_safe: discard dynamic check after init Brian Gerst
2016-01-16 19:36 ` Borislav Petkov
2016-01-16 19:58 ` Brian Gerst
2016-01-17 10:33 ` Borislav Petkov
2016-01-18 16:52 ` Brian Gerst
2016-01-18 17:49 ` Andy Lutomirski [this message]
2016-01-18 18:14 ` Borislav Petkov
2016-01-18 18:29 ` Andy Lutomirski
2016-01-18 18:39 ` Borislav Petkov
2016-01-18 19:45 ` H. Peter Anvin
2016-01-18 23:05 ` Borislav Petkov
2016-01-18 23:13 ` H. Peter Anvin
2016-01-18 23:25 ` Borislav Petkov
2016-01-19 13:57 ` Borislav Petkov
2016-01-19 16:23 ` Borislav Petkov
2016-01-19 23:10 ` Borislav Petkov
2016-01-19 23:26 ` Andy Lutomirski
2016-01-19 23:49 ` Boris Petkov
2016-01-20 4:03 ` H. Peter Anvin
2016-01-20 10:33 ` Borislav Petkov
2016-01-20 10:41 ` H. Peter Anvin
2016-01-21 22:14 ` Borislav Petkov
2016-01-21 22:22 ` H. Peter Anvin
2016-01-21 22:56 ` Borislav Petkov
2016-01-21 23:36 ` H. Peter Anvin
2016-01-21 23:37 ` H. Peter Anvin
2016-01-22 10:32 ` Borislav Petkov
2016-01-18 18:51 ` Borislav Petkov
2016-01-19 1:10 ` Borislav Petkov
2016-01-19 1:33 ` H. Peter Anvin
2016-01-19 9:22 ` Borislav Petkov
2016-01-20 4:02 ` H. Peter Anvin
2016-01-20 4:39 ` Brian Gerst
2016-01-20 4:42 ` H. Peter Anvin
2016-01-20 10:50 ` Borislav Petkov
2016-01-20 10:55 ` H. Peter Anvin
2016-01-20 11:05 ` Borislav Petkov
2016-01-20 14:48 ` H. Peter Anvin
2016-01-20 15:01 ` Borislav Petkov
2016-01-20 15:09 ` H. Peter Anvin
2016-01-20 16:04 ` Borislav Petkov
2016-01-20 16:16 ` H. Peter Anvin
2016-01-23 6:50 [PATCH] x86/head_64.S: do not use temporary register to check alignment Alexander Kuleshov
2016-01-26 9:31 ` Borislav Petkov
2016-01-26 21:12 [PATCH 00/10] tip-queue 2016-01-26, rest Borislav Petkov
2016-01-26 21:12 ` [PATCH 01/10] x86/asm: Add condition codes clobber to memory barrier macros Borislav Petkov
2016-01-26 21:12 ` [PATCH 02/10] x86/asm: Drop a comment left over from X86_OOSTORE Borislav Petkov
2016-01-26 21:12 ` [PATCH 03/10] x86/asm: Tweak the comment about wmb() use for IO Borislav Petkov
2016-01-26 21:12 ` [PATCH 04/10] x86/cpufeature: Carve out X86_FEATURE_* Borislav Petkov
2016-01-30 13:18 ` [tip:x86/asm] " tip-bot for Borislav Petkov
2016-01-26 21:12 ` [PATCH 05/10] x86/cpufeature: Replace the old static_cpu_has() with safe variant Borislav Petkov
2016-01-30 13:19 ` [tip:x86/asm] " tip-bot for Borislav Petkov
2016-01-26 21:12 ` [PATCH 06/10] x86/cpufeature: Get rid of the non-asm goto variant Borislav Petkov
2016-01-27 3:36 ` Brian Gerst
2016-01-27 8:41 ` Borislav Petkov
2016-01-27 8:43 ` [PATCH -v1.1 " Borislav Petkov
2016-01-30 13:19 ` [tip:x86/asm] " tip-bot for Borislav Petkov
2016-01-27 8:45 ` [PATCH -v1.1 8/10] x86/alternatives: Discard dynamic check after init Borislav Petkov
2016-01-30 13:20 ` [tip:x86/asm] " tip-bot for Brian Gerst
2016-01-26 21:12 ` [PATCH 07/10] x86/alternatives: Add an auxilary section Borislav Petkov
2016-01-30 13:19 ` [tip:x86/asm] " tip-bot for Borislav Petkov
2016-01-26 21:12 ` [PATCH 08/10] x86/alternatives: Discard dynamic check after init Borislav Petkov
2016-01-26 21:12 ` [PATCH 09/10] x86/vdso: Use static_cpu_has() Borislav Petkov
2016-01-30 13:20 ` [tip:x86/asm] " tip-bot for Borislav Petkov
2016-01-26 21:12 ` [PATCH 10/10] x86/head_64: Simplify kernel load address alignment check Borislav Petkov
2016-01-30 13:20 ` [tip:x86/boot] x86/boot: " tip-bot for Alexander Kuleshov
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