linux-kernel - Re: [PATCH v2] crypto/x86: Use CRC32 mnemonic in crc32c-intel

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Date:   Fri, 21 Aug 2020 17:57:21 +1000
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     Uros Bizjak <ubizjak@...il.com>
Cc:     linux-crypto@...r.kernel.org, x86@...nel.org,
        linux-kernel@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v2] crypto/x86: Use CRC32 mnemonic in crc32c-intel_glue.c

On Wed, Aug 05, 2020 at 01:17:29PM +0200, Uros Bizjak wrote:
> Current minimum required version of binutils is 2.23,
> which supports CRC32 instruction mnemonic.
> 
> Replace the byte-wise specification of CRC32 with this proper mnemonic.
> The compiler is now able to pass memory operand to the instruction,
> so there is no need for a temporary register anymore.
> 
> Some examples of the improvement:
> 
>  12a:	48 8b 08             	mov    (%rax),%rcx
>  12d:	f2 48 0f 38 f1 f1    	crc32q %rcx,%rsi
>  133:	48 83 c0 08          	add    $0x8,%rax
>  137:	48 39 d0             	cmp    %rdx,%rax
>  13a:	75 ee                	jne    12a <crc32c_intel_update+0x1a>
> 
> to:
> 
>  125:	f2 48 0f 38 f1 06    	crc32q (%rsi),%rax
>  12b:	48 83 c6 08          	add    $0x8,%rsi
>  12f:	48 39 d6             	cmp    %rdx,%rsi
>  132:	75 f1                	jne    125 <crc32c_intel_update+0x15>
> 
> and:
> 
>  146:	0f b6 08             	movzbl (%rax),%ecx
>  149:	f2 0f 38 f0 f1       	crc32b %cl,%esi
>  14e:	48 83 c0 01          	add    $0x1,%rax
>  152:	48 39 d0             	cmp    %rdx,%rax
>  155:	75 ef                	jne    146 <crc32c_intel_update+0x36>
> 
> to:
> 
>  13b:	f2 0f 38 f0 02       	crc32b (%rdx),%eax
>  140:	48 83 c2 01          	add    $0x1,%rdx
>  144:	48 39 ca             	cmp    %rcx,%rdx
>  147:	75 f2                	jne    13b <crc32c_intel_update+0x2b>
> 
> As the compiler has some more freedom w.r.t. register allocation,
> there is also a couple of reg-reg moves removed.
> 
> There are no hidden states for CRC32 insn, so there is no need to mark
> assembly as volatile.
> 
> v2: Introduce CRC32_INST define.
> 
> Signed-off-by: Uros Bizjak <ubizjak@...il.com>
> CC: Herbert Xu <herbert@...dor.apana.org.au>
> CC: "David S. Miller" <davem@...emloft.net>
> CC: Thomas Gleixner <tglx@...utronix.de>
> CC: Ingo Molnar <mingo@...hat.com>
> CC: Borislav Petkov <bp@...en8.de>
> CC: "H. Peter Anvin" <hpa@...or.com>
> ---
>  arch/x86/crypto/crc32c-intel_glue.c | 18 ++++++------------
>  1 file changed, 6 insertions(+), 12 deletions(-)

Patch applied.  Thanks.
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt