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From: "Jan Beulich" <JBeulich@suse.com>
To: xen-devel <xen-devel@lists.xenproject.org>
Cc: George Dunlap <George.Dunlap@eu.citrix.com>,
	Julien Grall <julien.grall@arm.com>,
	Stefano Stabellini <sstabellini@kernel.org>
Subject: [PATCH RFC 3/4] Arm64: further speed-up to hweight{32, 64}()
Date: Fri, 31 May 2019 03:53:39 -0600	[thread overview]
Message-ID: <5CF0F9A30200007800233E07@prv1-mh.provo.novell.com> (raw)
In-Reply-To: <5CF0F8530200007800233DE0@prv1-mh.provo.novell.com>

According to Linux commit e75bef2a4f ("arm64: Select
ARCH_HAS_FAST_MULTIPLIER") this is a further improvement over the
variant using only bitwise operations on at least some hardware, and no
worse on other.

Suggested-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
---
RFC: To be honest I'm not fully convinced this is a win in particular in
     the hweight32() case, as there's no actual shift insn which gets
     replaced by the multiplication. Even for hweight64() the compiler
     could emit better code and avoid the explicit shift by 32 (which it
     emits at least for me).

--- a/xen/arch/arm/Kconfig
+++ b/xen/arch/arm/Kconfig
@@ -12,6 +12,7 @@ config ARM_32
 config ARM_64
 	def_bool y
 	depends on 64BIT
+	select HAS_FAST_MULTIPLY
 
 config ARM
 	def_bool y



_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xenproject.org
https://lists.xenproject.org/mailman/listinfo/xen-devel

WARNING: multiple messages have this Message-ID (diff)
From: "Jan Beulich" <JBeulich@suse.com>
To: "xen-devel" <xen-devel@lists.xenproject.org>
Cc: George Dunlap <George.Dunlap@eu.citrix.com>,
	Julien Grall <julien.grall@arm.com>,
	Stefano Stabellini <sstabellini@kernel.org>
Subject: [Xen-devel] [PATCH RFC 3/4] Arm64: further speed-up to hweight{32, 64}()
Date: Fri, 31 May 2019 03:53:39 -0600	[thread overview]
Message-ID: <5CF0F9A30200007800233E07@prv1-mh.provo.novell.com> (raw)
Message-ID: <20190531095339.n0sdf7yr8q9-mzfeqa3poVK0y3Z-pOI4GZ9VqUDEsxM@z> (raw)
In-Reply-To: <5CF0F8530200007800233DE0@prv1-mh.provo.novell.com>

According to Linux commit e75bef2a4f ("arm64: Select
ARCH_HAS_FAST_MULTIPLIER") this is a further improvement over the
variant using only bitwise operations on at least some hardware, and no
worse on other.

Suggested-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
---
RFC: To be honest I'm not fully convinced this is a win in particular in
     the hweight32() case, as there's no actual shift insn which gets
     replaced by the multiplication. Even for hweight64() the compiler
     could emit better code and avoid the explicit shift by 32 (which it
     emits at least for me).

--- a/xen/arch/arm/Kconfig
+++ b/xen/arch/arm/Kconfig
@@ -12,6 +12,7 @@ config ARM_32
 config ARM_64
 	def_bool y
 	depends on 64BIT
+	select HAS_FAST_MULTIPLY
 
 config ARM
 	def_bool y



_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xenproject.org
https://lists.xenproject.org/mailman/listinfo/xen-devel

  parent reply	other threads:[~2019-05-31  9:53 UTC|newest]

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-31  9:48 [PATCH 0/4] bitops: hweight<N>() improvements Jan Beulich
2019-05-31  9:48 ` [Xen-devel] " Jan Beulich
2019-05-31  9:51 ` [PATCH 1/4] bitops: speed up hweight<N>() Jan Beulich
2019-05-31  9:51   ` [Xen-devel] " Jan Beulich
2019-05-31 19:40   ` Andrew Cooper
2019-05-31 19:40     ` [Xen-devel] " Andrew Cooper
2019-06-03  7:50     ` Jan Beulich
2019-06-03  7:50       ` [Xen-devel] " Jan Beulich
2019-06-03 10:02     ` Jan Beulich
2019-06-03 10:02       ` [Xen-devel] " Jan Beulich
2019-06-03 10:04       ` Andrew Cooper
2019-06-03 10:04         ` [Xen-devel] " Andrew Cooper
2019-05-31  9:52 ` [PATCH 2/4] x86: further speed-up to hweight{32,64}() Jan Beulich
2019-05-31  9:52   ` [Xen-devel] " Jan Beulich
2019-05-31 19:23   ` [PATCH 2/4] x86: further speed-up to hweight{32, 64}() Andrew Cooper
2019-05-31 19:23     ` [Xen-devel] " Andrew Cooper
2019-06-03  7:52     ` Jan Beulich
2019-06-03  7:52       ` [Xen-devel] " Jan Beulich
2019-05-31  9:53 ` Jan Beulich [this message]
2019-05-31  9:53   ` [Xen-devel] [PATCH RFC 3/4] Arm64: " Jan Beulich
2019-06-04 16:11   ` Julien Grall
2019-06-04 17:30     ` Robin Murphy
2019-06-05  7:42     ` Jan Beulich
2019-06-05  9:24       ` Julien Grall
2019-06-05  9:59         ` Jan Beulich
2019-06-05 11:05           ` Julien Grall
2019-06-06 15:29         ` Julien Grall
2019-05-31  9:54 ` [PATCH 4/4] x86: use POPCNT for hweight<N>() when available Jan Beulich
2019-05-31  9:54   ` [Xen-devel] " Jan Beulich
2019-05-31 20:43   ` Andrew Cooper
2019-05-31 20:43     ` [Xen-devel] " Andrew Cooper
2019-06-03  8:13     ` Jan Beulich
2019-06-03  8:13       ` [Xen-devel] " Jan Beulich
2019-06-04  6:08       ` Jan Beulich
2019-06-04  6:08         ` [Xen-devel] " Jan Beulich
2019-06-04 19:07       ` Andrew Cooper
2019-06-05  8:52         ` Jan Beulich

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