Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Message-Id: <2e730f4e6ef77be2d5bfc38273d8a622e2cb4f97.1579196675.git.christophe.leroy@c-s.fr>
In-Reply-To: <cover.1579196675.git.christophe.leroy@c-s.fr>
References: <cover.1579196675.git.christophe.leroy@c-s.fr>
From:   Christophe Leroy <christophe.leroy@c-s.fr>
Subject: [RFC PATCH v4 06/11] powerpc/vdso: provide inline alternative to
 __get_datapage()
To:     Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>, nathanl@linux.ibm.com,
        arnd@arndb.de, tglx@linutronix.de, vincenzo.frascino@arm.com,
        luto@kernel.org
Cc:     linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        linux-arm-kernel@lists.infradead.org, linux-mips@vger.kernel.org,
        x86@kernel.org
Date:   Thu, 16 Jan 2020 17:58:30 +0000 (UTC)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

__get_datapage() is only a few instructions to retrieve the
address of the page where the kernel stores data to the VDSO.

By inlining this function into its users, a bl/blr pair and
a mflr/mtlr pair is avoided, plus a few reg moves.

The improvement is noticeable (about 55 nsec/call on an 8xx)

With current __get_datapage() function:
gettimeofday:    vdso: 731 nsec/call
clock-gettime-realtime-coarse:    vdso: 668 nsec/call
clock-gettime-monotonic-coarse:    vdso: 745 nsec/call

Using the __get_datapage macro provided by this patch:
gettimeofday:    vdso: 677 nsec/call
clock-gettime-realtime-coarse:    vdso: 613 nsec/call
clock-gettime-monotonic-coarse:    vdso: 690 nsec/call

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
---
 arch/powerpc/include/asm/vdso_datapage.h | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/arch/powerpc/include/asm/vdso_datapage.h b/arch/powerpc/include/asm/vdso_datapage.h
index 4d7965bf369e..7342cc0c1ae4 100644
--- a/arch/powerpc/include/asm/vdso_datapage.h
+++ b/arch/powerpc/include/asm/vdso_datapage.h
@@ -105,6 +105,17 @@ struct vdso_arch_data {
 
 extern struct vdso_arch_data *vdso_data;
 
+#else /* __ASSEMBLY__ */
+
+.macro get_datapage ptr, offset=0
+	bcl	20, 31, .+4
+	mflr	\ptr
+#if CONFIG_PPC_PAGE_SHIFT > 14
+	addis	\ptr, \ptr, (_vdso_datapage + \offset - (.-4))@ha
+#endif
+	addi	\ptr, \ptr, (_vdso_datapage + \offset - (.-4))@l
+.endm
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* __KERNEL__ */
-- 
2.13.3