Re: [PATCH v2] MIPS: Check __clang__ to avoid performance influence with GCC in csum_tcpudp_nofold()

[Tiezhu Yang]

On 03/15/2021 06:24 PM, Alexander Lobakin wrote:

From: Tiezhu Yang <yangtie...@loongson.cn>
Date: Tue, 9 Mar 2021 12:18:13 +0800

The asm code in csum_tcpudp_nofold() is performance-critical, I am sorry
for the poorly considered implementation about the performance influence
with GCC in the commit 198688edbf77 ("MIPS: Fix inline asm input/output
type mismatch in checksum.h used with Clang").

With this patch, we can build successfully by both GCC and Clang,
at the same time, we can avoid the potential performance influence
with GCC.

Signed-off-by: Tiezhu Yang <yangtie...@loongson.cn>
---
  arch/mips/include/asm/checksum.h | 12 ++++++++----
  1 file changed, 8 insertions(+), 4 deletions(-)

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__

Why not rely on CONFIG_CC_IS_CLANG here?

Hi,

Thanks for your suggestion, I once considered that way:
https://lore.kernel.org/patchwork/patch/1371666/#1587127

But it still occurs build error under CC_IS_GCC when
make M=samples/bpf which used with Clang compiler,
so use __clang__ is better.

Thanks,
Tiezhu

+       unsigned long sum = (__force unsigned long)sum_in;
+#else
+       __wsum sum = sum_in;
+#endif

        __asm__(
        "  .set    push            # csum_tcpudp_nofold\n"
@@ -159,7 +163,7 @@ static inline __wsum csum_tcpudp_nofold(__be32 saddr, 
__be32 daddr,
        "  addu    %0, $1          \n"
  #endif
        "  .set    pop"
-       : "=r" (tmp)
+       : "=r" (sum)
        : "0" ((__force unsigned long)daddr),
          "r" ((__force unsigned long)saddr),
  #ifdef __MIPSEL__
@@ -169,7 +173,7 @@ static inline __wsum csum_tcpudp_nofold(__be32 saddr, 
__be32 daddr,
  #endif
          "r" ((__force unsigned long)sum));

-       return (__force __wsum)tmp;
+       return (__force __wsum)sum;
  }
  #define csum_tcpudp_nofold csum_tcpudp_nofold

--
2.1.0

Al