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Message-ID: <bdfe753d-0ef2-8f66-7716-acadfc3917a5@loongson.cn>
Date: Mon, 15 Mar 2021 20:26:05 +0800
From: Tiezhu Yang <yangtiezhu@...ngson.cn>
To: "Maciej W. Rozycki" <macro@...am.me.uk>
Cc: Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org,
Xuefeng Li <lixuefeng@...ngson.cn>,
David Laight <David.Laight@...LAB.COM>
Subject: Re: [PATCH v2] MIPS: Check __clang__ to avoid performance influence
with GCC in csum_tcpudp_nofold()
On 03/15/2021 04:49 AM, Maciej W. Rozycki wrote:
> On Tue, 9 Mar 2021, Tiezhu Yang wrote:
>
>> diff --git a/arch/mips/include/asm/checksum.h b/arch/mips/include/asm/checksum.h
>> index 1e6c135..80eddd4 100644
>> --- a/arch/mips/include/asm/checksum.h
>> +++ b/arch/mips/include/asm/checksum.h
>> @@ -128,9 +128,13 @@ static inline __sum16 ip_fast_csum(const void *iph, unsigned int ihl)
>>
>> static inline __wsum csum_tcpudp_nofold(__be32 saddr, __be32 daddr,
>> __u32 len, __u8 proto,
>> - __wsum sum)
>> + __wsum sum_in)
>> {
>> - unsigned long tmp = (__force unsigned long)sum;
>> +#ifdef __clang__
>> + unsigned long sum = (__force unsigned long)sum_in;
>> +#else
>> + __wsum sum = sum_in;
>> +#endif
> This looks much better to me, but I'd keep the variable names unchanged
> as `sum_in' isn't used beyond the initial assignment anyway (you'll have
> to update the references with asm operands accordingly of course).
>
> Have you verified that code produced by GCC remains the same with your
> change in place as it used to be up to commit 198688edbf77? I can see no
> such information in the commit description whether here or in the said
> commit.
>
> Maciej
Hi Maciej,
Thanks for your reply.
gcc --version
gcc (Debian 10.2.1-6) 10.2.1 20210110
net/ipv4/tcp_ipv4.c
tcp_v4_send_reset()
csum_tcpudp_nofold()
objdump -d vmlinux > vmlinux.dump
(1) Before commit 198688edbf77
("MIPS: Fix inline asm input/output type mismatch in checksum.h used
with Clang"):
ffffffff80aa835c: 00004025 move a4,zero
ffffffff80aa8360: 92020012 lbu v0,18(s0)
ffffffff80aa8364: de140030 ld s4,48(s0)
ffffffff80aa8368: 0064182d daddu v1,v1,a0
ffffffff80aa836c: 304200ff andi v0,v0,0xff
ffffffff80aa8370: 9c64000c lwu a0,12(v1)
ffffffff80aa8374: 9c660010 lwu a2,16(v1)
ffffffff80aa8378: afa70038 sw a3,56(sp)
ffffffff80aa837c: 24071a00 li a3,6656
ffffffff80aa8380: 0086202d daddu a0,a0,a2
ffffffff80aa8384: 0087202d daddu a0,a0,a3
ffffffff80aa8388: 0088202d daddu a0,a0,a4
ffffffff80aa838c: 0004083c dsll32 at,a0,0x0
ffffffff80aa8390: 0081202d daddu a0,a0,at
ffffffff80aa8394: 0081082b sltu at,a0,at
ffffffff80aa8398: 0004203f dsra32 a0,a0,0x0
ffffffff80aa839c: 00812021 addu a0,a0,at
(2) After commit 198688edbf77
("MIPS: Fix inline asm input/output type mismatch in checksum.h used
with Clang"):
ffffffff80aa836c: 00004025 move a4,zero
ffffffff80aa8370: 92040012 lbu a0,18(s0)
ffffffff80aa8374: de140030 ld s4,48(s0)
ffffffff80aa8378: 0062182d daddu v1,v1,v0
ffffffff80aa837c: 308400ff andi a0,a0,0xff
ffffffff80aa8380: 9c62000c lwu v0,12(v1)
ffffffff80aa8384: 9c660010 lwu a2,16(v1)
ffffffff80aa8388: afa70038 sw a3,56(sp)
ffffffff80aa838c: 24071a00 li a3,6656
ffffffff80aa8390: 0046102d daddu v0,v0,a2
ffffffff80aa8394: 0047102d daddu v0,v0,a3
ffffffff80aa8398: 0048102d daddu v0,v0,a4
ffffffff80aa839c: 0002083c dsll32 at,v0,0x0
ffffffff80aa83a0: 0041102d daddu v0,v0,at
ffffffff80aa83a4: 0041082b sltu at,v0,at
ffffffff80aa83a8: 0002103f dsra32 v0,v0,0x0
ffffffff80aa83ac: 00411021 addu v0,v0,at
(3) With this patch:
ffffffff80aa835c: 00004025 move a4,zero
ffffffff80aa8360: 92020012 lbu v0,18(s0)
ffffffff80aa8364: de140030 ld s4,48(s0)
ffffffff80aa8368: 0064182d daddu v1,v1,a0
ffffffff80aa836c: 304200ff andi v0,v0,0xff
ffffffff80aa8370: 9c64000c lwu a0,12(v1)
ffffffff80aa8374: 9c660010 lwu a2,16(v1)
ffffffff80aa8378: afa70038 sw a3,56(sp)
ffffffff80aa837c: 24071a00 li a3,6656
ffffffff80aa8380: 0086202d daddu a0,a0,a2
ffffffff80aa8384: 0087202d daddu a0,a0,a3
ffffffff80aa8388: 0088202d daddu a0,a0,a4
ffffffff80aa838c: 0004083c dsll32 at,a0,0x0
ffffffff80aa8390: 0081202d daddu a0,a0,at
ffffffff80aa8394: 0081082b sltu at,a0,at
ffffffff80aa8398: 0004203f dsra32 a0,a0,0x0
ffffffff80aa839c: 00812021 addu a0,a0,at
(4) With the following changes based on commit 198688edbf77
("MIPS: Fix inline asm input/output type mismatch in checksum.h used
with Clang"):
diff --git a/arch/mips/include/asm/checksum.h
b/arch/mips/include/asm/checksum.h
index 1e6c135..e1f80407 100644
--- a/arch/mips/include/asm/checksum.h
+++ b/arch/mips/include/asm/checksum.h
@@ -130,7 +130,11 @@ static inline __wsum csum_tcpudp_nofold(__be32
saddr, __be32 daddr,
__u32 len, __u8 proto,
__wsum sum)
{
+#ifdef __clang__
unsigned long tmp = (__force unsigned long)sum;
+#else
+ __wsum tmp = sum;
+#endif
__asm__(
" .set push # csum_tcpudp_nofold\n"
ffffffff80aa835c: 00004025 move a4,zero
ffffffff80aa8360: 92020012 lbu v0,18(s0)
ffffffff80aa8364: de140030 ld s4,48(s0)
ffffffff80aa8368: 0064182d daddu v1,v1,a0
ffffffff80aa836c: 304200ff andi v0,v0,0xff
ffffffff80aa8370: 9c64000c lwu a0,12(v1)
ffffffff80aa8374: 9c660010 lwu a2,16(v1)
ffffffff80aa8378: afa70038 sw a3,56(sp)
ffffffff80aa837c: 24071a00 li a3,6656
ffffffff80aa8380: 0086202d daddu a0,a0,a2
ffffffff80aa8384: 0087202d daddu a0,a0,a3
ffffffff80aa8388: 0088202d daddu a0,a0,a4
ffffffff80aa838c: 0004083c dsll32 at,a0,0x0
ffffffff80aa8390: 0081202d daddu a0,a0,at
ffffffff80aa8394: 0081082b sltu at,a0,at
ffffffff80aa8398: 0004203f dsra32 a0,a0,0x0
ffffffff80aa839c: 00812021 addu a0,a0,at
The code produced by GCC remains the same between (1), (3) and (4),
the last changes looks like better (with less changes based on commit
198688edbf77), so I will send v3 later.
Thanks,
Tiezhu
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