linux-kernel - [PATCH v4 1/3] x86/mce: Avoid unnecessary padding in struct mce

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Message-ID: <20220225193342.215780-2-Smita.KoralahalliChannabasappa@amd.com>
Date:   Fri, 25 Feb 2022 13:33:40 -0600
From:   Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>
To:     <x86@...nel.org>, <linux-edac@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
CC:     Tony Luck <tony.luck@...el.com>, "H . Peter Anvin" <hpa@...or.com>,
        "Dave Hansen" <dave.hansen@...ux.intel.com>,
        James Morse <james.morse@....com>,
        Robert Richter <rric@...nel.org>,
        Yazen Ghannam <yazen.ghannam@....com>,
        Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>
Subject: [PATCH v4 1/3] x86/mce: Avoid unnecessary padding in struct mce_bank

Convert struct mce_bank member "init" from bool to a bitfield to get rid
of unnecessary padding.

Outputs collected before and after the change.

$ pahole -C mce_bank arch/x86/kernel/cpu/mce/core.o

before:

	/* size: 16, cachelines: 1, members: 2 */
	/* padding: 7 */
	/* last cacheline: 16 bytes */

after:

	/* size: 16, cachelines: 1, members: 3 */
	/* last cacheline: 16 bytes */

No functional changes.

Signed-off-by: Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>
---
Link:
https://lkml.kernel.org/r/20220211223442.254489-5-Smita.KoralahalliChannabasappa@amd.com

v4:
	Moved this patch to the first in the series.
---
 arch/x86/kernel/cpu/mce/core.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c
index 728f3b36ce2d..c0e9aa9c8749 100644
--- a/arch/x86/kernel/cpu/mce/core.c
+++ b/arch/x86/kernel/cpu/mce/core.c
@@ -69,7 +69,9 @@ DEFINE_PER_CPU_READ_MOSTLY(unsigned int, mce_num_banks);
 
 struct mce_bank {
 	u64			ctl;			/* subevents to enable */
-	bool			init;			/* initialise bank? */
+
+	__u64 init			: 1,		/* initialise bank? */
+	      __reserved_1		: 63;
 };
 static DEFINE_PER_CPU_READ_MOSTLY(struct mce_bank[MAX_NR_BANKS], mce_banks_array);
 
-- 
2.17.1