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Mon, 9 Oct 2023 15:14:18 +0000 (UTC) Received: from mgamail.intel.com (mgamail.intel.com [134.134.136.126]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-651-a8JbGZ6aN4uYvbFwCh72tg-4; Mon, 09 Oct 2023 11:14:17 -0400 X-MC-Unique: a8JbGZ6aN4uYvbFwCh72tg-4 X-IronPort-AV: E=McAfee;i="6600,9927,10858"; a="369232068" X-IronPort-AV: E=Sophos;i="6.03,210,1694761200"; d="scan'208";a="369232068" Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by orsmga106.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 09 Oct 2023 08:13:14 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10858"; a="869287957" X-IronPort-AV: E=Sophos;i="6.03,210,1694761200"; d="scan'208";a="869287957" Received: from newjersey.igk.intel.com ([10.102.20.203]) by fmsmga002.fm.intel.com with ESMTP; 09 Oct 2023 08:13:11 -0700 From: Alexander Lobakin To: Yury Norov Date: Mon, 9 Oct 2023 17:10:15 +0200 Message-ID: <20231009151026.66145-4-aleksander.lobakin@intel.com> In-Reply-To: <20231009151026.66145-1-aleksander.lobakin@intel.com> References: <20231009151026.66145-1-aleksander.lobakin@intel.com> MIME-Version: 1.0 X-Mimecast-Impersonation-Protect: Policy=CLT - Impersonation Protection Definition; Similar Internal Domain=false; Similar Monitored External Domain=false; Custom External Domain=false; Mimecast External Domain=false; Newly Observed Domain=false; Internal User Name=false; Custom Display Name List=false; Reply-to Address Mismatch=false; Targeted Threat Dictionary=false; Mimecast Threat Dictionary=false; Custom Threat Dictionary=false X-Scanned-By: MIMEDefang 3.1 on 10.11.54.4 X-Mailman-Approved-At: Tue, 10 Oct 2023 07:02:50 +0000 Subject: [dm-devel] [PATCH 03/14] bitops: let the compiler optimize __assign_bit() X-BeenThere: dm-devel@redhat.com X-Mailman-Version: 2.1.29 Precedence: list List-Id: device-mapper development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-s390@vger.kernel.org, ntfs3@lists.linux.dev, Przemek Kitszel , David Ahern , Rasmus Villemoes , dm-devel@redhat.com, linux-kernel@vger.kernel.org, Alexander Lobakin , Eric Dumazet , netdev@vger.kernel.org, Alexander Potapenko , Simon Horman , Jakub Kicinski , Andy Shevchenko , linux-btrfs@vger.kernel.org Errors-To: dm-devel-bounces@redhat.com Sender: "dm-devel" X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.7 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: intel.com Since commit b03fc1173c0c ("bitops: let optimize out non-atomic bitops on compile-time constants"), the compilers are able to expand inline bitmap operations to compile-time initializers when possible. However, during the round of replacement if-__set-else-__clear with __assign_bit() as per Andy's advice, bloat-o-meter showed +1024 bytes difference in object code size for one module (even one function), where the pattern: DECLARE_BITMAP(foo) = { }; // on the stack, zeroed if (a) __set_bit(const_bit_num, foo); if (b) __set_bit(another_const_bit_num, foo); ... is heavily used, although there should be no difference: the bitmap is zeroed, so the second half of __assign_bit() should be compiled-out as a no-op. I either missed the fact that __assign_bit() has bitmap pointer marked as `volatile` (as we usually do for bitmaps) or was hoping that the compilers would at least try to look past the `volatile` for __always_inline functions. Anyhow, due to that attribute, the compilers were always compiling the whole expression and no mentioned compile-time optimizations were working. Convert __assign_bit() to a macro since it's a very simple if-else and all of the checks are performed inside __set_bit() and __clear_bit(), thus that wrapper has to be as transparent as possible. After that change, despite it showing only -20 bytes change for vmlinux (due to that it's still relatively unpopular), no drastic code size changes happen when replacing if-set-else-clear for onstack bitmaps with __assign_bit(), meaning the compiler now expands them to the actual operations will all the expected optimizations. Cc: Andy Shevchenko Reviewed-by: Przemek Kitszel Signed-off-by: Alexander Lobakin --- include/linux/bitops.h | 10 ++-------- 1 file changed, 2 insertions(+), 8 deletions(-) diff --git a/include/linux/bitops.h b/include/linux/bitops.h index e0cd09eb91cd..f98f4fd1047f 100644 --- a/include/linux/bitops.h +++ b/include/linux/bitops.h @@ -284,14 +284,8 @@ static __always_inline void assign_bit(long nr, volatile unsigned long *addr, clear_bit(nr, addr); } -static __always_inline void __assign_bit(long nr, volatile unsigned long *addr, - bool value) -{ - if (value) - __set_bit(nr, addr); - else - __clear_bit(nr, addr); -} +#define __assign_bit(nr, addr, value) \ + ((value) ? __set_bit(nr, addr) : __clear_bit(nr, addr)) /** * __ptr_set_bit - Set bit in a pointer's value