The following commit has been merged into the x86/core branch of tip: Commit-ID: d31c3c683ee668ba5d87c0730610442fd672525f Gitweb: https://git.kernel.org/tip/d31c3c683ee668ba5d87c0730610442fd672525f Author: Eric Dumazet <edumazet@xxxxxxxxxx> AuthorDate: Fri, 12 Nov 2021 08:19:50 -08:00 Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx> CommitterDate: Wed, 17 Nov 2021 14:48:54 +01:00 x86/csum: Rewrite/optimize csum_partial() With more NIC supporting CHECKSUM_COMPLETE, and IPv6 being widely used. csum_partial() is heavily used with small amount of bytes, and is consuming many cycles. IPv6 header size for instance is 40 bytes. Another thing to consider is that NET_IP_ALIGN is 0 on x86, meaning that network headers are not word-aligned, unless the driver forces this. This means that csum_partial() fetches one u16 to 'align the buffer', then perform three u64 additions with carry in a loop, then a remaining u32, then a remaining u16. With this new version, we perform a loop only for the 64 bytes blocks, then the remaining is bisected. Tested on various cpus, all of them show a big reduction in csum_partial() cost (by 50 to 80 %) Before: 4.16% [kernel] [k] csum_partial After: 0.83% [kernel] [k] csum_partial If run in a loop 1,000,000 times: Before: 26,922,913 cycles # 3846130.429 GHz 80,302,961 instructions # 2.98 insn per cycle 21,059,816 branches # 3008545142.857 M/sec 2,896 branch-misses # 0.01% of all branches After: 17,960,709 cycles # 3592141.800 GHz 41,292,805 instructions # 2.30 insn per cycle 11,058,119 branches # 2211623800.000 M/sec 2,997 branch-misses # 0.03% of all branches Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Reviewed-by: Alexander Duyck <alexanderduyck@xxxxxx> Link: https://lore.kernel.org/r/20211112161950.528886-1-eric.dumazet@xxxxxxxxx --- arch/x86/lib/csum-partial_64.c | 162 +++++++++++++------------------- 1 file changed, 67 insertions(+), 95 deletions(-) diff --git a/arch/x86/lib/csum-partial_64.c b/arch/x86/lib/csum-partial_64.c index e7925d6..5ec3562 100644 --- a/arch/x86/lib/csum-partial_64.c +++ b/arch/x86/lib/csum-partial_64.c @@ -9,6 +9,7 @@ #include <linux/compiler.h> #include <linux/export.h> #include <asm/checksum.h> +#include <asm/word-at-a-time.h> static inline unsigned short from32to16(unsigned a) { @@ -21,120 +22,92 @@ static inline unsigned short from32to16(unsigned a) } /* - * Do a 64-bit checksum on an arbitrary memory area. + * Do a checksum on an arbitrary memory area. * Returns a 32bit checksum. * * This isn't as time critical as it used to be because many NICs * do hardware checksumming these days. - * - * Things tried and found to not make it faster: - * Manual Prefetching - * Unrolling to an 128 bytes inner loop. - * Using interleaving with more registers to break the carry chains. + * + * Still, with CHECKSUM_COMPLETE this is called to compute + * checksums on IPv6 headers (40 bytes) and other small parts. + * it's best to have buff aligned on a 64-bit boundary */ -static unsigned do_csum(const unsigned char *buff, unsigned len) +__wsum csum_partial(const void *buff, int len, __wsum sum) { - unsigned odd, count; - unsigned long result = 0; + u64 temp64 = (__force u64)sum; + unsigned odd, result; - if (unlikely(len == 0)) - return result; odd = 1 & (unsigned long) buff; if (unlikely(odd)) { - result = *buff << 8; + if (unlikely(len == 0)) + return sum; + temp64 += (*(unsigned char *)buff << 8); len--; buff++; } - count = len >> 1; /* nr of 16-bit words.. */ - if (count) { - if (2 & (unsigned long) buff) { - result += *(unsigned short *)buff; - count--; - len -= 2; - buff += 2; - } - count >>= 1; /* nr of 32-bit words.. */ - if (count) { - unsigned long zero; - unsigned count64; - if (4 & (unsigned long) buff) { - result += *(unsigned int *) buff; - count--; - len -= 4; - buff += 4; - } - count >>= 1; /* nr of 64-bit words.. */ - /* main loop using 64byte blocks */ - zero = 0; - count64 = count >> 3; - while (count64) { - asm("addq 0*8(%[src]),%[res]\n\t" - "adcq 1*8(%[src]),%[res]\n\t" - "adcq 2*8(%[src]),%[res]\n\t" - "adcq 3*8(%[src]),%[res]\n\t" - "adcq 4*8(%[src]),%[res]\n\t" - "adcq 5*8(%[src]),%[res]\n\t" - "adcq 6*8(%[src]),%[res]\n\t" - "adcq 7*8(%[src]),%[res]\n\t" - "adcq %[zero],%[res]" - : [res] "=r" (result) - : [src] "r" (buff), [zero] "r" (zero), - "[res]" (result)); - buff += 64; - count64--; - } + while (unlikely(len >= 64)) { + asm("addq 0*8(%[src]),%[res]\n\t" + "adcq 1*8(%[src]),%[res]\n\t" + "adcq 2*8(%[src]),%[res]\n\t" + "adcq 3*8(%[src]),%[res]\n\t" + "adcq 4*8(%[src]),%[res]\n\t" + "adcq 5*8(%[src]),%[res]\n\t" + "adcq 6*8(%[src]),%[res]\n\t" + "adcq 7*8(%[src]),%[res]\n\t" + "adcq $0,%[res]" + : [res] "+r" (temp64) + : [src] "r" (buff) + : "memory"); + buff += 64; + len -= 64; + } + + if (len & 32) { + asm("addq 0*8(%[src]),%[res]\n\t" + "adcq 1*8(%[src]),%[res]\n\t" + "adcq 2*8(%[src]),%[res]\n\t" + "adcq 3*8(%[src]),%[res]\n\t" + "adcq $0,%[res]" + : [res] "+r" (temp64) + : [src] "r" (buff) + : "memory"); + buff += 32; + } + if (len & 16) { + asm("addq 0*8(%[src]),%[res]\n\t" + "adcq 1*8(%[src]),%[res]\n\t" + "adcq $0,%[res]" + : [res] "+r" (temp64) + : [src] "r" (buff) + : "memory"); + buff += 16; + } + if (len & 8) { + asm("addq 0*8(%[src]),%[res]\n\t" + "adcq $0,%[res]" + : [res] "+r" (temp64) + : [src] "r" (buff) + : "memory"); + buff += 8; + } + if (len & 7) { + unsigned int shift = (8 - (len & 7)) * 8; + unsigned long trail; - /* last up to 7 8byte blocks */ - count %= 8; - while (count) { - asm("addq %1,%0\n\t" - "adcq %2,%0\n" - : "=r" (result) - : "m" (*(unsigned long *)buff), - "r" (zero), "0" (result)); - --count; - buff += 8; - } - result = add32_with_carry(result>>32, - result&0xffffffff); + trail = (load_unaligned_zeropad(buff) << shift) >> shift; - if (len & 4) { - result += *(unsigned int *) buff; - buff += 4; - } - } - if (len & 2) { - result += *(unsigned short *) buff; - buff += 2; - } + asm("addq %[trail],%[res]\n\t" + "adcq $0,%[res]" + : [res] "+r" (temp64) + : [trail] "r" (trail)); } - if (len & 1) - result += *buff; - result = add32_with_carry(result>>32, result & 0xffffffff); + result = add32_with_carry(temp64 >> 32, temp64 & 0xffffffff); if (unlikely(odd)) { result = from32to16(result); result = ((result >> 8) & 0xff) | ((result & 0xff) << 8); } - return result; -} - -/* - * computes the checksum of a memory block at buff, length len, - * and adds in "sum" (32-bit) - * - * returns a 32-bit number suitable for feeding into itself - * or csum_tcpudp_magic - * - * this function must be called with even lengths, except - * for the last fragment, which may be odd - * - * it's best to have buff aligned on a 64-bit boundary - */ -__wsum csum_partial(const void *buff, int len, __wsum sum) -{ - return (__force __wsum)add32_with_carry(do_csum(buff, len), - (__force u32)sum); + return (__force __wsum)result; } EXPORT_SYMBOL(csum_partial); @@ -147,4 +120,3 @@ __sum16 ip_compute_csum(const void *buff, int len) return csum_fold(csum_partial(buff,len,0)); } EXPORT_SYMBOL(ip_compute_csum); -
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