| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Date: Wed, 10 Nov 2021 22:53:22 -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>
Subject: [RFC] 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 in RX path are not word-aligned,
unless the driver forces this.
This means that csum_partial() fetches one u16
to 'align the buffer', then perform seven u64 additions
with carry in a loop, then a remaining u32, then a remaining u16.
With this new version, we perform 10 u32 adds with carry, to
avoid the expensive 64->32 transformation. Using 5 u64 adds
plus one add32_with_carry() is more expensive.
Also note that this avoids loops for less than ~60 bytes.
Tested on various cpus, all of them show a big reduction in
csum_partial() cost (by 30 to 75 %)
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Alexander Duyck <alexander.duyck@...il.com>
---
arch/x86/lib/csum-partial_64.c | 146 +++++++++++++++++----------------
1 file changed, 77 insertions(+), 69 deletions(-)
diff --git a/arch/x86/lib/csum-partial_64.c b/arch/x86/lib/csum-partial_64.c
index e7925d668b680269fb2442766deaf416dc42f9a1..f48fe0ec9663ff3afa1b5403f135407b8b0fde01 100644
--- a/arch/x86/lib/csum-partial_64.c
+++ b/arch/x86/lib/csum-partial_64.c
@@ -21,97 +21,105 @@ 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.
*/
static unsigned do_csum(const unsigned char *buff, unsigned len)
{
- unsigned odd, count;
- unsigned long result = 0;
+ unsigned long dwords;
+ unsigned odd, result = 0;
- if (unlikely(len == 0))
- return result;
odd = 1 & (unsigned long) buff;
if (unlikely(odd)) {
+ if (unlikely(len == 0))
+ return result;
result = *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.. */
+ if (unlikely(len >= 64)) {
+ unsigned long temp64 = result;
+ do {
+ asm(" addq 0*8(%[src]),%[res]\n"
+ " adcq 1*8(%[src]),%[res]\n"
+ " adcq 2*8(%[src]),%[res]\n"
+ " adcq 3*8(%[src]),%[res]\n"
+ " adcq 4*8(%[src]),%[res]\n"
+ " adcq 5*8(%[src]),%[res]\n"
+ " adcq 6*8(%[src]),%[res]\n"
+ " adcq 7*8(%[src]),%[res]\n"
+ " adcq $0,%[res]"
+ : [res] "=r" (temp64)
+ : [src] "r" (buff), "[res]" (temp64)
+ : "memory");
+ buff += 64;
+ len -= 64;
+ } while (len >= 64);
+ result = add32_with_carry(temp64 >> 32, temp64 & 0xffffffff);
+ }
- /* 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--;
- }
+ dwords = len >> 2;
+ if (dwords) { /* dwords is in [1..15] */
+ unsigned long dest;
- /* 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);
+ /*
+ * This implements an optimized version of
+ * switch (dwords) {
+ * case 15: res = add_with_carry(res, buf32[14]); fallthrough;
+ * case 14: res = add_with_carry(res, buf32[13]); fallthrough;
+ * case 13: res = add_with_carry(res, buf32[12]); fallthrough;
+ * ...
+ * case 3: res = add_with_carry(res, buf32[2]); fallthrough;
+ * case 2: res = add_with_carry(res, buf32[1]); fallthrough;
+ * case 1: res = add_with_carry(res, buf32[0]); fallthrough;
+ * }
+ *
+ * "adcl 8byteoff(%reg1),%reg2" are using either 3 or 4 bytes.
+ */
+ asm(" call 1f\n"
+ "1: pop %[dest]\n"
+ " lea (2f-1b)(%[dest],%[skip],4),%[dest]\n"
+ " clc\n"
+ " jmp *%[dest]\n .align 4\n"
+ "2:\n"
+ " adcl 14*4(%[src]),%[res]\n .align 4\n"
+ " adcl 13*4(%[src]),%[res]\n .align 4\n"
+ " adcl 12*4(%[src]),%[res]\n .align 4\n"
+ " adcl 11*4(%[src]),%[res]\n .align 4\n"
+ " adcl 10*4(%[src]),%[res]\n .align 4\n"
+ " adcl 9*4(%[src]),%[res]\n .align 4\n"
+ " adcl 8*4(%[src]),%[res]\n .align 4\n"
+ " adcl 7*4(%[src]),%[res]\n .align 4\n"
+ " adcl 6*4(%[src]),%[res]\n .align 4\n"
+ " adcl 5*4(%[src]),%[res]\n .align 4\n"
+ " adcl 4*4(%[src]),%[res]\n .align 4\n"
+ " adcl 3*4(%[src]),%[res]\n .align 4\n"
+ " adcl 2*4(%[src]),%[res]\n .align 4\n"
+ " adcl 1*4(%[src]),%[res]\n .align 4\n"
+ " adcl 0*4(%[src]),%[res]\n"
+ " adcl $0,%[res]"
+ : [res] "=r" (result), [dest] "=&r" (dest)
+ : [src] "r" (buff), "[res]" (result),
+ [skip] "r" (dwords ^ 15)
+ : "memory");
+ }
- if (len & 4) {
- result += *(unsigned int *) buff;
- buff += 4;
- }
- }
+ if (len & 3U) {
+ buff += len & ~3U;
+ result = from32to16(result);
if (len & 2) {
result += *(unsigned short *) buff;
buff += 2;
}
+ if (len & 1)
+ result += *buff;
}
- if (len & 1)
- result += *buff;
- result = add32_with_carry(result>>32, result & 0xffffffff);
if (unlikely(odd)) {
result = from32to16(result);
result = ((result >> 8) & 0xff) | ((result & 0xff) << 8);
--
2.34.0.rc0.344.g81b53c2807-goog
Powered by blists - more mailing lists