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Date: Fri, 12 Nov 2021 08:19:50 -0800
From: Eric Dumazet <eric.dumazet@...il.com>
To: "David S . Miller" <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>
Cc: netdev <netdev@...r.kernel.org>,
Eric Dumazet <edumazet@...gle.com>,
Eric Dumazet <eric.dumazet@...il.com>, x86@...nel.org,
Alexander Duyck <alexander.duyck@...il.com>,
Peter Zijlstra <peterz@...radead.org>,
Andrew Cooper <andrew.cooper3@...rix.com>
Subject: [PATCH v2] x86/csum: rewrite csum_partial()
From: Eric Dumazet <edumazet@...gle.com>
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 %)
v3: - use "+r" (temp64) asm constraints (Andrew).
- fold do_csum() in csum_partial(), as gcc does not inline it.
- fix bug added in v2 for the "odd" case.
- back using addcq, as Andrew pointed the clang bug that was adding
a stall on my hosts.
(separate patch to add32_with_carry() will follow)
- use load_unaligned_zeropad() for final 1-7 bytes (Peter & Alexander).
v2: - removed the hard-coded switch(), as it was not RETPOLINE aware.
- removed the final add32_with_carry() that we were doing
in csum_partial(), we can simply pass @sum to do_csum().
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Alexander Duyck <alexander.duyck@...il.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Andrew Cooper <andrew.cooper3@...rix.com>
---
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 e7925d668b680269fb2442766deaf416dc42f9a1..5ec35626945b6db2f7f41c6d46d5e422810eac46 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);
-
--
2.34.0.rc1.387.gb447b232ab-goog
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