linux-kernel - Re: [RFC PATCH 3/3] x86/cpufeature: Remove unused and seldomly used cpu_has

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Message-ID: <20151127180432.GC27739@pd.tnic>
Date:	Fri, 27 Nov 2015 19:04:33 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Josh Triplett <josh@...htriplett.org>
Cc:	X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andy Lutomirski <luto@...capital.net>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Matt Mackall <mpm@...enic.com>, Chris Mason <clm@...com>,
	Josef Bacik <jbacik@...com>, David Sterba <dsterba@...e.com>,
	kbuild test robot <fengguang.wu@...el.com>
Subject: Re: [RFC PATCH 3/3] x86/cpufeature: Remove unused and seldomly used
 cpu_has_xx macros

On Fri, Nov 27, 2015 at 02:52:57PM +0100, Borislav Petkov wrote:
> commit						.TEXT 	.DATA 	.BSS
> rc2+							650055 	127948 	1189128
> 0a53df8a1a3a ("x86/cpufeature: Move some of the...") 	649863 	127948 	1189384
> ed03a85e6575 ("x86/cpufeature: Cleanup get_cpu_cap()") 	649831 	127948 	1189384
> acde56aeda14 ("x86/cpufeature: Remove unused and...")	649831 	127948 	1189384
> 
> I'll look at doing the macro thing now, hopefully it doesn't get too ugly.

Yeah, we do save us some ~1.6K text (cf numbers above) for the price
of a bit slower feature bit testing. Don't know if it matters at all,
though:

commit							.TEXT 	.DATA 	.BSS
CONFIG_X86_FAST_FEATURE_TESTS				648209	127948	1189384

and diff looks pretty simple:

---
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 4a9b9a9a1a64..ff64585ea0bf 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -350,6 +350,10 @@ config X86_FEATURE_NAMES
 
 	  If in doubt, say Y.
 
+config X86_FAST_FEATURE_TESTS
+	bool "Fast feature tests" if EMBEDDED
+	default y
+
 config X86_X2APIC
 	bool "Support x2apic"
 	depends on X86_LOCAL_APIC && X86_64 && (IRQ_REMAP || HYPERVISOR_GUEST)
diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
index cbe390044a7c..7ad8c9464297 100644
--- a/arch/x86/include/asm/cpufeature.h
+++ b/arch/x86/include/asm/cpufeature.h
@@ -410,7 +410,7 @@ extern const char * const x86_bug_flags[NBUGINTS*32];
  * fast paths and boot_cpu_has() otherwise!
  */
 
-#if __GNUC__ >= 4
+#if __GNUC__ >= 4 && defined(CONFIG_X86_FAST_FEATURE_TESTS)
 extern void warn_pre_alternatives(void);
 extern bool __static_cpu_has_safe(u16 bit);

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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