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d="scan'208";a="97179658" From: Andrew Cooper To: Xen-devel CC: Andrew Cooper , Jan Beulich , =?UTF-8?q?Roger=20Pau=20Monn=C3=A9?= , Wei Liu Subject: [PATCH 2/2] x86/irq: Improve local_irq_restore() code generation and performance Date: Mon, 20 Feb 2023 19:47:02 +0000 Message-ID: <20230220194702.2260181-3-andrew.cooper3@citrix.com> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20230220194702.2260181-1-andrew.cooper3@citrix.com> References: <20230220194702.2260181-1-andrew.cooper3@citrix.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable X-ZohoMail-DKIM: pass (identity @citrix.com) X-ZM-MESSAGEID: 1676922475580100003 POPF is a horribly expensive instruction, while STI is an optimised fastpat= h. Switching POPF for a conditional branch and STI caused an 8% perf improveme= nt in various linux measurements. While I don't expect the change to be that dramatic in Xen, there will be an improvement. Furthermore, there is the following code generation improvement: add/remove: 0/0 grow/shrink: 3/52 up/down: 52/-966 (-914) owing to not needing to opencode the restriction to just IF in asm. Signed-off-by: Andrew Cooper --- CC: Jan Beulich CC: Roger Pau Monn=C3=A9 CC: Wei Liu --- xen/arch/x86/include/asm/system.h | 9 ++------- 1 file changed, 2 insertions(+), 7 deletions(-) diff --git a/xen/arch/x86/include/asm/system.h b/xen/arch/x86/include/asm/s= ystem.h index 65e63de69a67..4be235472ecd 100644 --- a/xen/arch/x86/include/asm/system.h +++ b/xen/arch/x86/include/asm/system.h @@ -267,13 +267,8 @@ static inline unsigned long array_index_mask_nospec(un= signed long index, }) #define local_irq_restore(x) \ ({ \ - BUILD_BUG_ON(sizeof(x) !=3D sizeof(long)); \ - asm volatile ( "pushfq\n\t" \ - "andq %0, (%%rsp)\n\t" \ - "orq %1, (%%rsp)\n\t" \ - "popfq" \ - : : "i?r" ( ~X86_EFLAGS_IF ), \ - "ri" ( (x) & X86_EFLAGS_IF ) ); \ + if ( (x) & X86_EFLAGS_IF ) \ + local_irq_enable(); \ }) =20 static inline int local_irq_is_enabled(void) --=20 2.30.2