linux-kernel - Re: [PATCH v2 2/2] sparc64: Use lzcnt instruction for fls and _

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Message-Id: <9DB110D2-67D6-4CAA-8C14-C3AF995D9711@oracle.com>
Date:   Wed, 27 Sep 2017 14:45:34 -0700
From:   Anthony Yznaga <anthony.yznaga@...cle.com>
To:     Sam Ravnborg <sam@...nborg.org>
Cc:     Vijay Kumar <vijay.ac.kumar@...cle.com>, davem@...emloft.net,
        linux-kernel@...r.kernel.org, sparclinux@...r.kernel.org,
        babu.moger@...cle.com, rob.gardner@...cle.com
Subject: Re: [PATCH v2 2/2] sparc64: Use lzcnt instruction for fls and __fls


> On Sep 27, 2017, at 12:56 PM, Sam Ravnborg <sam@...nborg.org> wrote:
> 
> Hi Vijay.
> 
> On Wed, Sep 27, 2017 at 01:25:26PM -0600, Vijay Kumar wrote:
>> For T4 and above, patch fls and __fls functions
>> at the boot time to use lzcnt instruction.
>> 
>> Signed-off-by: Vijay Kumar <vijay.ac.kumar@...cle.com>
>> Reviewed-by: Babu Moger <babu.moger@...cle.com>
>> ---
>> arch/sparc/Makefile         |    1 +
>> arch/sparc/kernel/head_64.S |    2 ++
>> arch/sparc/lib/Makefile     |    3 +++
>> arch/sparc/lib/NG4fls.S     |   30 ++++++++++++++++++++++++++++++
>> arch/sparc/lib/NG4patch.S   |    9 +++++++++
>> 5 files changed, 45 insertions(+), 0 deletions(-)
>> 
>> diff --git a/arch/sparc/Makefile b/arch/sparc/Makefile
>> index 8496a07..0763cd8 100644
>> --- a/arch/sparc/Makefile
>> +++ b/arch/sparc/Makefile
>> @@ -48,6 +48,7 @@ KBUILD_CFLAGS += -ffixed-g4 -ffixed-g5 -fcall-used-g7 -Wno-sign-compare
>> KBUILD_CFLAGS += -Wa,--undeclared-regs
>> KBUILD_CFLAGS += $(call cc-option,-mtune=ultrasparc3)
>> KBUILD_AFLAGS += -m64 -mcpu=ultrasparc -Wa,--undeclared-regs
>> +KBUILD_AFLAGS += -Wa,-Asparc4
> This change is not justified anywhere??

It looks like this is to get the assembler to recognize the lzcnt instruction.

Vijay,
Older assemblers may not support this flag so you’ll need to hardcode the lzcnt instructions using .word directives.

Anthony

> 
>> 
>> ifeq ($(CONFIG_MCOUNT),y)
>>   KBUILD_CFLAGS += -pg
>> diff --git a/arch/sparc/kernel/head_64.S b/arch/sparc/kernel/head_64.S
>> index 78e0211..1165254 100644
>> --- a/arch/sparc/kernel/head_64.S
>> +++ b/arch/sparc/kernel/head_64.S
>> @@ -628,6 +628,8 @@ niagara4_patch:
>> 	 nop
>> 	call	niagara4_patch_pageops
>> 	 nop
>> +	call	niagara4_patch_fls
>> +	 nop
>> 
>> 	ba,a,pt	%xcc, 80f
>> 	 nop
>> diff --git a/arch/sparc/lib/Makefile b/arch/sparc/lib/Makefile
>> index eefbb9c..72d2d8c 100644
>> --- a/arch/sparc/lib/Makefile
>> +++ b/arch/sparc/lib/Makefile
>> @@ -46,3 +46,6 @@ lib-$(CONFIG_SPARC64) += mcount.o ipcsum.o xor.o hweight.o ffs.o
>> obj-$(CONFIG_SPARC64) += iomap.o
>> obj-$(CONFIG_SPARC32) += atomic32.o ucmpdi2.o
>> obj-$(CONFIG_SPARC64) += PeeCeeI.o
>> +
>> +obj-$(CONFIG_SPARC64) += fls.o
>> +obj-$(CONFIG_SPARC64) += NG4fls.o
>> diff --git a/arch/sparc/lib/NG4fls.S b/arch/sparc/lib/NG4fls.S
>> new file mode 100644
>> index 0000000..eb239aa
>> --- /dev/null
>> +++ b/arch/sparc/lib/NG4fls.S
>> @@ -0,0 +1,30 @@
>> +/* NG4fls.S: SPARC optimized fls and __fls for T4 and above.
>> + *
>> + * Copyright (c) 2017, Oracle and/or its affiliates. All rights reserved.
>> + */
>> +
>> +	.text
>> +	.align 32
>> +
>> +	.globl NG4fls
>> +	.globl __NG4fls
>> +	.type  NG4fls, #function
>> +	.type  __NG4fls, #function
> 
> Use ENTRY(), ENDPROC() as already mentioned.
>> +NG4fls:
>> +	lzcnt   %o0, %o1
>> +	mov     64, %o2
>> +	retl
>> +	 sub     %o2, %o1, %o0
>> +	.size   NG4fls, .-NG4fls
>> +
>> +__NG4fls:
>> +	brz,pn  %o0, 1f
>> +        mov	%o0, %o1
> Use tabs for indent, not spaces. In this case one tab + one space.
> 
>> +	lzcnt	%o1, %o0
>> +	mov     63, %o2
>> +	sub     %o2, %o0, %o0
>> +1:
>> +	retl
>> +	 nop
>> +	.size   __NG4fls, .-__NG4fls
>> diff --git a/arch/sparc/lib/NG4patch.S b/arch/sparc/lib/NG4patch.S
>> index 3cc0f8c..1010d53 100644
>> --- a/arch/sparc/lib/NG4patch.S
>> +++ b/arch/sparc/lib/NG4patch.S
>> @@ -52,3 +52,12 @@ niagara4_patch_pageops:
>> 	retl
>> 	 nop
>> 	.size	niagara4_patch_pageops,.-niagara4_patch_pageops
>> +
>> +	.globl	niagara4_patch_fls
>> +	.type	niagara4_patch_fls,#function
>> +niagara4_patch_fls:
>> +	NG_DO_PATCH(fls, NG4fls)
>> +	NG_DO_PATCH(__fls, __NG4fls)
>> +	retl
>> +	 nop
>> +	.size	niagara4_patch_fls,.-niagara4_patch_fls
> 
> Please path the remaining functions in this file with ENTRY(), ENDPROC() - in a separate patch.
> 
> 	Sam
> --
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