[PATCH net-next v2 0/2] ovs: introduce arch-specific fast hashing improvements

[PATCH net-next v2 0/2] ovs: introduce arch-specific fast hashing improvements

[Francesco Fusco]

From: Daniel Borkmann <dborkman@redhat.com>

We are introducing a fast hash function (see patch1) that can be
used in the context of OpenVSwitch to reduce the hashing footprint
(patch2). For details, please see individual patches!

Thanks !

v1->v2:
 - Make hash generic and place it under lib

Francesco Fusco (2):
  lib: introduce arch optimized hash library
  net: ovs: use CRC32 accelerated flow hash if available

 arch/x86/include/asm/hash.h  |  7 ++++
 arch/x86/lib/Makefile        |  2 +-
 arch/x86/lib/hash.c          | 88 ++++++++++++++++++++++++++++++++++++++++++++
 include/asm-generic/hash.h   |  9 +++++
 include/linux/hash.h         | 36 ++++++++++++++++++
 lib/Makefile                 |  2 +-
 lib/hash.c                   | 38 +++++++++++++++++++
 net/openvswitch/flow_table.c |  4 +-
 8 files changed, 182 insertions(+), 4 deletions(-)
 create mode 100644 arch/x86/include/asm/hash.h
 create mode 100644 arch/x86/lib/hash.c
 create mode 100644 include/asm-generic/hash.h
 create mode 100644 lib/hash.c

-- 
1.8.3.1

[PATCH net-next v2 1/2] lib: introduce arch optimized hash library

[Francesco Fusco]

We introduce a new hashing library that is meant to be used in
the contexts where speed is more important than uniformity of the
hashed values. The hash library leverages architecture specific
implementation to achieve high performance and fall backs to
jhash() for the generic case.

On Intel-based x86 architectures, the library can exploit the crc32l
instruction, part of the Intel SSE4.2 instruction set, if the
instruction is supported by the processor. This implementation
is twice as fast as the jhash() implementation on an i7 processor.

Additional architectures, such as Arm64 provide instructions for
accelerating the computation of CRC, so they could be added as well
in follow-up work.

Signed-off-by: Francesco Fusco <ffusco-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Signed-off-by: Daniel Borkmann <dborkman-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Signed-off-by: Thomas Graf <tgraf-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Cc: linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
---
 arch/x86/include/asm/hash.h |  7 ++++
 arch/x86/lib/Makefile       |  2 +-
 arch/x86/lib/hash.c         | 88 +++++++++++++++++++++++++++++++++++++++++++++
 include/asm-generic/hash.h  |  9 +++++
 include/linux/hash.h        | 36 +++++++++++++++++++
 lib/Makefile                |  2 +-
 lib/hash.c                  | 38 ++++++++++++++++++++
 7 files changed, 180 insertions(+), 2 deletions(-)
 create mode 100644 arch/x86/include/asm/hash.h
 create mode 100644 arch/x86/lib/hash.c
 create mode 100644 include/asm-generic/hash.h
 create mode 100644 lib/hash.c

diff --git a/arch/x86/include/asm/hash.h b/arch/x86/include/asm/hash.h
new file mode 100644
index 0000000..e8c58f8
--- /dev/null
+++ b/arch/x86/include/asm/hash.h
@@ -0,0 +1,7 @@
+#ifndef _ASM_X86_HASH_H
+#define _ASM_X86_HASH_H
+
+struct fast_hash_ops;
+extern void setup_arch_fast_hash(struct fast_hash_ops *ops);
+
+#endif /* _ASM_X86_HASH_H */
diff --git a/arch/x86/lib/Makefile b/arch/x86/lib/Makefile
index 992d63b..eabcb6e 100644
--- a/arch/x86/lib/Makefile
+++ b/arch/x86/lib/Makefile
@@ -24,7 +24,7 @@ lib-$(CONFIG_SMP) += rwlock.o
 lib-$(CONFIG_RWSEM_XCHGADD_ALGORITHM) += rwsem.o
 lib-$(CONFIG_INSTRUCTION_DECODER) += insn.o inat.o
 
-obj-y += msr.o msr-reg.o msr-reg-export.o
+obj-y += msr.o msr-reg.o msr-reg-export.o hash.o
 
 ifeq ($(CONFIG_X86_32),y)
         obj-y += atomic64_32.o
diff --git a/arch/x86/lib/hash.c b/arch/x86/lib/hash.c
new file mode 100644
index 0000000..3056702
--- /dev/null
+++ b/arch/x86/lib/hash.c
@@ -0,0 +1,88 @@
+/*
+ * Some portions derived from code covered by the following notice:
+ *
+ * Copyright (c) 2010-2013 Intel Corporation. All rights reserved.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ *   * Redistributions of source code must retain the above copyright
+ *     notice, this list of conditions and the following disclaimer.
+ *   * Redistributions in binary form must reproduce the above copyright
+ *     notice, this list of conditions and the following disclaimer in
+ *     the documentation and/or other materials provided with the
+ *     distribution.
+ *   * Neither the name of Intel Corporation nor the names of its
+ *     contributors may be used to endorse or promote products derived
+ *     from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <linux/hash.h>
+
+#include <asm/processor.h>
+#include <asm/cpufeature.h>
+#include <asm/hash.h>
+
+static inline u32 crc32_u32(u32 crc, u32 val)
+{
+	asm ("crc32l %1,%0\n" : "+r" (crc) : "rm" (val));
+	return crc;
+}
+
+static u32 intel_crc4_2_hash(const void *data, u32 len, u32 seed)
+{
+	const u32 *p32 = (const u32 *) data;
+	u32 i, tmp = 0;
+
+	for (i = 0; i < len / 4; i++)
+		seed = crc32_u32(*p32++, seed);
+
+	switch (3 - (len & 0x03)) {
+	case 0:
+		tmp |= *((const u8 *) p32 + 2) << 16;
+		/* fallthrough */
+	case 1:
+		tmp |= *((const u8 *) p32 + 1) << 8;
+		/* fallthrough */
+	case 2:
+		tmp |= *((const u8 *) p32);
+		seed = crc32_u32(tmp, seed);
+	default:
+		break;
+	}
+
+	return seed;
+}
+
+static u32 intel_crc4_2_hash2(const u32 *data, u32 len, u32 seed)
+{
+	const u32 *p32 = (const u32 *) data;
+	u32 i;
+
+	for (i = 0; i < len; i++)
+		seed = crc32_u32(*p32++, seed);
+
+	return seed;
+}
+
+void setup_arch_fast_hash(struct fast_hash_ops *ops)
+{
+	if (cpu_has_xmm4_2) {
+		ops->hash  = intel_crc4_2_hash;
+		ops->hash2 = intel_crc4_2_hash2;
+	}
+}
diff --git a/include/asm-generic/hash.h b/include/asm-generic/hash.h
new file mode 100644
index 0000000..05cb342
--- /dev/null
+++ b/include/asm-generic/hash.h
@@ -0,0 +1,9 @@
+#ifndef __ASM_GENERIC_HASH_H
+#define __ASM_GENERIC_HASH_H
+
+struct arch_hash_ops;
+static inline void setup_arch_fast_hash(struct arch_hash_ops *ops)
+{
+}
+
+#endif /* __ASM_GENERIC_HASH_H */
diff --git a/include/linux/hash.h b/include/linux/hash.h
index f09a0ae..bd1754c 100644
--- a/include/linux/hash.h
+++ b/include/linux/hash.h
@@ -15,6 +15,7 @@
  */
 
 #include <asm/types.h>
+#include <asm/hash.h>
 #include <linux/compiler.h>
 
 /* 2^31 + 2^29 - 2^25 + 2^22 - 2^19 - 2^16 + 1 */
@@ -78,4 +79,39 @@ static inline u32 hash32_ptr(const void *ptr)
 #endif
 	return (u32)val;
 }
+
+struct fast_hash_ops {
+	u32 (*hash)(const void *data, u32 len, u32 seed);
+	u32 (*hash2)(const u32 *data, u32 len, u32 seed);
+};
+
+/**
+ *	arch_fast_hash - Caclulates a hash over a given buffer that can have
+ *			 arbitrary size. This function will eventually use an
+ *			 architecture-optimized hashing implementation if
+ *			 available, and trades off distribution for speed.
+ *
+ *	@data: buffer to hash
+ *	@len: length of buffer in bytes
+ *	@seed: start seed
+ *
+ *	Returns 32bit hash.
+ */
+extern u32 arch_fast_hash(const void *data, u32 len, u32 seed);
+
+/**
+ *	arch_fast_hash2 - Caclulates a hash over a given buffer that has a
+ *			  size that is of a multiple of 32bit words. This
+ *			  function will eventually use an architecture-
+ *			  optimized hashing implementation if available,
+ *			  and trades off distribution for speed.
+ *
+ *	@data: buffer to hash (must be 32bit padded)
+ *	@len: number of 32bit words
+ *	@seed: start seed
+ *
+ *	Returns 32bit hash.
+ */
+extern u32 arch_fast_hash2(const u32 *data, u32 len, u32 seed);
+
 #endif /* _LINUX_HASH_H */
diff --git a/lib/Makefile b/lib/Makefile
index a459c31..d0f79c5 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -26,7 +26,7 @@ obj-y += bcd.o div64.o sort.o parser.o halfmd4.o debug_locks.o random32.o \
 	 bust_spinlocks.o hexdump.o kasprintf.o bitmap.o scatterlist.o \
 	 gcd.o lcm.o list_sort.o uuid.o flex_array.o iovec.o clz_ctz.o \
 	 bsearch.o find_last_bit.o find_next_bit.o llist.o memweight.o kfifo.o \
-	 percpu-refcount.o percpu_ida.o
+	 percpu-refcount.o percpu_ida.o hash.o
 obj-y += string_helpers.o
 obj-$(CONFIG_TEST_STRING_HELPERS) += test-string_helpers.o
 obj-y += kstrtox.o
diff --git a/lib/hash.c b/lib/hash.c
new file mode 100644
index 0000000..b89f06a
--- /dev/null
+++ b/lib/hash.c
@@ -0,0 +1,38 @@
+/* General purpose hashing library
+ *
+ * That's a start of a kernel hashing library, which can be extended
+ * with further algorithms in future. arch_fast_hash{2,}() will
+ * eventually resolve to an architecture optimized implementation.
+ *
+ * Copyright 2013 Francesco Fusco <ffusco-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
+ * Copyright 2013 Daniel Borkmann <dborkman-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
+ * Copyright 2013 Thomas Graf <tgraf-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
+ * Licensed under the GNU General Public License, version 2.0 (GPLv2)
+ */
+
+#include <linux/jhash.h>
+#include <linux/hash.h>
+
+static struct fast_hash_ops arch_hash_ops __read_mostly = {
+	.hash  = jhash,
+	.hash2 = jhash2,
+};
+
+u32 arch_fast_hash(const void *data, u32 len, u32 seed)
+{
+	return arch_hash_ops.hash(data, len, seed);
+}
+EXPORT_SYMBOL_GPL(arch_fast_hash);
+
+u32 arch_fast_hash2(const u32 *data, u32 len, u32 seed)
+{
+	return arch_hash_ops.hash2(data, len, seed);
+}
+EXPORT_SYMBOL_GPL(arch_fast_hash2);
+
+static int __init hashlib_init(void)
+{
+	setup_arch_fast_hash(&arch_hash_ops);
+	return 0;
+}
+early_initcall(hashlib_init);
-- 
1.8.3.1

Re: [PATCH net-next v2 1/2] lib: introduce arch optimized hash library

[Nicolas Dichtel]

Le 12/12/2013 16:09, Francesco Fusco a écrit :
> We introduce a new hashing library that is meant to be used in
> the contexts where speed is more important than uniformity of the
> hashed values. The hash library leverages architecture specific
> implementation to achieve high performance and fall backs to
> jhash() for the generic case.
>
> On Intel-based x86 architectures, the library can exploit the crc32l
> instruction, part of the Intel SSE4.2 instruction set, if the
> instruction is supported by the processor. This implementation
> is twice as fast as the jhash() implementation on an i7 processor.
>
> Additional architectures, such as Arm64 provide instructions for
> accelerating the computation of CRC, so they could be added as well
> in follow-up work.
>
> Signed-off-by: Francesco Fusco <ffusco@redhat.com>
> Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
> Signed-off-by: Thomas Graf <tgraf@redhat.com>
> Cc: linux-kernel@vger.kernel.org
> ---
>   arch/x86/include/asm/hash.h |  7 ++++
>   arch/x86/lib/Makefile       |  2 +-
>   arch/x86/lib/hash.c         | 88 +++++++++++++++++++++++++++++++++++++++++++++
>   include/asm-generic/hash.h  |  9 +++++
>   include/linux/hash.h        | 36 +++++++++++++++++++
>   lib/Makefile                |  2 +-
>   lib/hash.c                  | 38 ++++++++++++++++++++
>   7 files changed, 180 insertions(+), 2 deletions(-)
>   create mode 100644 arch/x86/include/asm/hash.h
>   create mode 100644 arch/x86/lib/hash.c
>   create mode 100644 include/asm-generic/hash.h
>   create mode 100644 lib/hash.c
>
> diff --git a/arch/x86/include/asm/hash.h b/arch/x86/include/asm/hash.h
> new file mode 100644
> index 0000000..e8c58f8
> --- /dev/null
> +++ b/arch/x86/include/asm/hash.h
> @@ -0,0 +1,7 @@
> +#ifndef _ASM_X86_HASH_H
> +#define _ASM_X86_HASH_H
> +
> +struct fast_hash_ops;
> +extern void setup_arch_fast_hash(struct fast_hash_ops *ops);
> +
> +#endif /* _ASM_X86_HASH_H */
> diff --git a/arch/x86/lib/Makefile b/arch/x86/lib/Makefile
> index 992d63b..eabcb6e 100644
> --- a/arch/x86/lib/Makefile
> +++ b/arch/x86/lib/Makefile
> @@ -24,7 +24,7 @@ lib-$(CONFIG_SMP) += rwlock.o
>   lib-$(CONFIG_RWSEM_XCHGADD_ALGORITHM) += rwsem.o
>   lib-$(CONFIG_INSTRUCTION_DECODER) += insn.o inat.o
>
> -obj-y += msr.o msr-reg.o msr-reg-export.o
> +obj-y += msr.o msr-reg.o msr-reg-export.o hash.o
>
>   ifeq ($(CONFIG_X86_32),y)
>           obj-y += atomic64_32.o
> diff --git a/arch/x86/lib/hash.c b/arch/x86/lib/hash.c
> new file mode 100644
> index 0000000..3056702
> --- /dev/null
> +++ b/arch/x86/lib/hash.c
> @@ -0,0 +1,88 @@
> +/*
> + * Some portions derived from code covered by the following notice:
> + *
> + * Copyright (c) 2010-2013 Intel Corporation. All rights reserved.
> + * All rights reserved.
Is it possible to trace that this comes from the DPDK?
At least in the commit log, like it was done in the v1.

> + *
> + * Redistribution and use in source and binary forms, with or without
> + * modification, are permitted provided that the following conditions
> + * are met:
> + *
> + *   * Redistributions of source code must retain the above copyright
> + *     notice, this list of conditions and the following disclaimer.
> + *   * Redistributions in binary form must reproduce the above copyright
> + *     notice, this list of conditions and the following disclaimer in
> + *     the documentation and/or other materials provided with the
> + *     distribution.
> + *   * Neither the name of Intel Corporation nor the names of its
> + *     contributors may be used to endorse or promote products derived
> + *     from this software without specific prior written permission.
> + *
> + * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
> + * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
> + * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
> + * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
> + * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
> + * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
> + * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
> + * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
> + * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
> + * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
> + * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
> + */
> +
> +#include <linux/hash.h>
> +
> +#include <asm/processor.h>
> +#include <asm/cpufeature.h>
> +#include <asm/hash.h>
> +
> +static inline u32 crc32_u32(u32 crc, u32 val)
> +{
> +	asm ("crc32l %1,%0\n" : "+r" (crc) : "rm" (val));
I'm not an expert, but is it not possible to use intrisics functions, like it is
done in the original code?


Regards,
Nicolas

Re: [PATCH net-next v2 1/2] lib: introduce arch optimized hash library

[Daniel Borkmann]

On 12/12/2013 06:54 PM, Nicolas Dichtel wrote:
...
> Is it possible to trace that this comes from the DPDK?
> At least in the commit log, like it was done in the v1.

Hm, that got lost; but we can put that back into the commit log.
In any case, we properly included the header comment, of course.

>> +static inline u32 crc32_u32(u32 crc, u32 val)
>> +{
>> +    asm ("crc32l %1,%0\n" : "+r" (crc) : "rm" (val));
> I'm not an expert, but is it not possible to use intrisics functions, like it is
> done in the original code?

Intrinsics are not used/available in the kernel, so we used asm
as everywhere else.

Re: [PATCH net-next v2 0/2] ovs: introduce arch-specific fast hashing improvements

[David Miller]

From: Francesco Fusco <ffusco-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Date: Thu, 12 Dec 2013 16:09:04 +0100

> From: Daniel Borkmann <dborkman-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
> 
> We are introducing a fast hash function (see patch1) that can be
> used in the context of OpenVSwitch to reduce the hashing footprint
> (patch2). For details, please see individual patches!
> 
> Thanks !
> 
> v1->v2:
>  - Make hash generic and place it under lib

Series applied, thanks.

[PATCH net-next v2 2/2] net: ovs: use CRC32 accelerated flow hash if available

[Francesco Fusco]

Currently OVS uses jhash2() for calculating flow hashes in its
internal flow_hash() function. The performance of the flow_hash()
function is critical, as the input data can be hundreds of bytes
long.

OVS is largely deployed in x86_64 based datacenters.  Therefore,
we argue that the performance critical fast path of OVS should
exploit underlying CPU features in order to reduce the per packet
processing costs. We replace jhash2 with the hash implementation
provided by the kernel hash lib, which exploits the crc32l
instruction to achieve high performance

Our patch greatly reduces the hash footprint from ~200 cycles of
jhash2() to around ~90 cycles in case of ovs_flow_hash_crc()
(measured with rdtsc over maximum length flow keys on an i7 Intel
CPU).

Additionally, we wrote a microbenchmark to stress the flow table
performance. The benchmark inserts random flows into the flow
hash and then performs lookups. Our hash deployed on a CRC32
capable CPU reduces the lookup for 1000 flows, 100 masks from
~10,100us to ~6,700us, for example.

Thus, simply use the newly introduced arch_fast_hash2() as a
drop-in replacement.

Signed-off-by: Francesco Fusco <ffusco@redhat.com>
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: Thomas Graf <tgraf@redhat.com>
---
 net/openvswitch/flow_table.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/openvswitch/flow_table.c b/net/openvswitch/flow_table.c
index e425427..0e720c3 100644
--- a/net/openvswitch/flow_table.c
+++ b/net/openvswitch/flow_table.c
@@ -25,7 +25,7 @@
 #include <linux/if_vlan.h>
 #include <net/llc_pdu.h>
 #include <linux/kernel.h>
-#include <linux/jhash.h>
+#include <linux/hash.h>
 #include <linux/jiffies.h>
 #include <linux/llc.h>
 #include <linux/module.h>
@@ -362,7 +362,7 @@ static u32 flow_hash(const struct sw_flow_key *key, int key_start,
 	/* Make sure number of hash bytes are multiple of u32. */
 	BUILD_BUG_ON(sizeof(long) % sizeof(u32));
 
-	return jhash2(hash_key, hash_u32s, 0);
+	return arch_fast_hash2(hash_key, hash_u32s, 0);
 }
 
 static int flow_key_start(const struct sw_flow_key *key)
-- 
1.8.3.1

Re: [PATCH net-next v2 2/2] net: ovs: use CRC32 accelerated flow hash if available

[Jesse Gross]

On Thu, Dec 12, 2013 at 7:09 AM, Francesco Fusco <ffusco@redhat.com> wrote:
> Currently OVS uses jhash2() for calculating flow hashes in its
> internal flow_hash() function. The performance of the flow_hash()
> function is critical, as the input data can be hundreds of bytes
> long.
>
> OVS is largely deployed in x86_64 based datacenters.  Therefore,
> we argue that the performance critical fast path of OVS should
> exploit underlying CPU features in order to reduce the per packet
> processing costs. We replace jhash2 with the hash implementation
> provided by the kernel hash lib, which exploits the crc32l
> instruction to achieve high performance
>
> Our patch greatly reduces the hash footprint from ~200 cycles of
> jhash2() to around ~90 cycles in case of ovs_flow_hash_crc()
> (measured with rdtsc over maximum length flow keys on an i7 Intel
> CPU).
>
> Additionally, we wrote a microbenchmark to stress the flow table
> performance. The benchmark inserts random flows into the flow
> hash and then performs lookups. Our hash deployed on a CRC32
> capable CPU reduces the lookup for 1000 flows, 100 masks from
> ~10,100us to ~6,700us, for example.
>
> Thus, simply use the newly introduced arch_fast_hash2() as a
> drop-in replacement.
>
> Signed-off-by: Francesco Fusco <ffusco@redhat.com>
> Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
> Signed-off-by: Thomas Graf <tgraf@redhat.com>

Acked-by: Jesse Gross <jesse@nicira.com>

Out of curiosity, did you try using crc32q? OVS data structures are
already aligned to 8 bytes. It would also be interesting to know if a
parallelized implementation is worthwhile, although my guess is that
the OVS flow key is not quite long enough.

Re: [PATCH net-next v2 2/2] net: ovs: use CRC32 accelerated flow hash if available

[Francesco Fusco]

On 12/12/2013 09:20 PM, Jesse Gross wrote:
> Out of curiosity, did you try using crc32q? OVS data structures are
> already aligned to 8 bytes. It would also be interesting to know if a
> parallelized implementation is worthwhile, although my guess is that
> the OVS flow key is not quite long enough.

We did not try with crc32q yet because we had the very same concerns.
In the general case, when the length of the key is not a multiple of 8 
bytes, we will have to use the crc32q to process multiple 64 bit 
numbers, then process the the rest with a crc32l. My guess is that the
performance benefit won't be that high.

But we will try that out and if the outcome will be positive, we will 
submit a follow up patch.

Best,
Francesco

Re: [PATCH net-next v2 2/2] net: ovs: use CRC32 accelerated flow hash if available

[Jesse Gross]

On Fri, Dec 13, 2013 at 1:55 AM, Francesco Fusco <ffusco@redhat.com> wrote:
> On 12/12/2013 09:20 PM, Jesse Gross wrote:
>>
>> Out of curiosity, did you try using crc32q? OVS data structures are
>> already aligned to 8 bytes. It would also be interesting to know if a
>> parallelized implementation is worthwhile, although my guess is that
>> the OVS flow key is not quite long enough.
>
>
> We did not try with crc32q yet because we had the very same concerns.
> In the general case, when the length of the key is not a multiple of 8
> bytes, we will have to use the crc32q to process multiple 64 bit numbers,
> then process the the rest with a crc32l. My guess is that the
> performance benefit won't be that high.

On 64-bit platforms, OVS already enforces alignment and multiples of 8
bytes for flow keys. If we introduced a hash primitive that does 8
bytes at a time instead of 4, there should be nothing extra to process
(although I don't know how big the upside would be).

Re: [PATCH net-next v2 2/2] net: ovs: use CRC32 accelerated flow hash if available

[David Laight]

> From: Jesse Gross
...
> Out of curiosity, did you try using crc32q? OVS data structures are
> already aligned to 8 bytes. It would also be interesting to know if a
> parallelized implementation is worthwhile, although my guess is that
> the OVS flow key is not quite long enough.

My thoughts exactly.
Given this is a hash it could crc alternate words into separate
accumulators and the combine the values at the end.
That way you are still doing sequential accesses to the data.
(The crc instruction might be better than an xor for the combine.)
If the cpu has 3 execution units that can do crc, use them all.

It might be that the hash function is now an insignificant cost.
Looking at how much hashing the data twice (discarding the first
result - assign to global volatile data) slows things down can
help determine this.

	David

Re: [PATCH net-next v2 2/2] net: ovs: use CRC32 accelerated flow hash if available

[Francesco Fusco]

On 12/13/2013 11:01 AM, David Laight wrote:
> My thoughts exactly.
> Given this is a hash it could crc alternate words into separate
> accumulators and the combine the values at the end.
> That way you are still doing sequential accesses to the data.
> (The crc instruction might be better than an xor for the combine.)
> If the cpu has 3 execution units that can do crc, use them all.
>
> It might be that the hash function is now an insignificant cost.
> Looking at how much hashing the data twice (discarding the first
> result - assign to global volatile data) slows things down can
> help determine this.

On i7 CPUs the crc32/crc64 instructions have a throughput
of 1 cycle and a latency of 3 cycles [1], which means that 1) with this 
code we pay 3 clocks per crc32 instruction, and 2) we could compute 
three CRCs in parallel, each processing 1/3 of the data during the same 
clock. This could in theory provide 3x the performance.

For short keys (~100 bytes and less) there is chance that the 3x 
theoretical speedup will be destroyed by the additional code required
to compute boundaries, xor the results, etc. But as I already mentioned, 
this is something to try.

[1] 
http://www.intel.com/content/dam/www/public/us/en/documents/white-papers/fast-crc-computation-paper.pdf

Re: [PATCH net-next v2 0/2] ovs: introduce arch-specific fast hashing improvements

[David Miller]

From: Francesco Fusco <ffusco@redhat.com>
Date: Thu, 12 Dec 2013 16:09:04 +0100

> We are introducing a fast hash function (see patch1) that can be
> used in the context of OpenVSwitch to reduce the hashing footprint
> (patch2). For details, please see individual patches!

No objections from my side, I'll let the x86 folks get a chance to
review this.  I can add this optimization on sparc64 chips that have
the crc instructions too.

I think we'll need to add implementations hash_3words, hash_2words,
and hash_1word when we try to take advantage of this in the networking
more generally.

[PATCH net-next v2 0/2] ovs: introduce arch-specific fast hashing improvements

[Francesco Fusco]

From: Daniel Borkmann <dborkman@redhat.com>

We are introducing a fast hash function (see patch1) that can be
used in the context of OpenVSwitch to reduce the hashing footprint
(patch2). For details, please see individual patches!

Thanks !

v1->v2:
 - Make hash generic and place it under lib

Francesco Fusco (2):
  lib: introduce arch optimized hash library
  net: ovs: use CRC32 accelerated flow hash if available

 arch/x86/include/asm/hash.h  |  7 ++++
 arch/x86/lib/Makefile        |  2 +-
 arch/x86/lib/hash.c          | 88 ++++++++++++++++++++++++++++++++++++++++++++
 include/asm-generic/hash.h   |  9 +++++
 include/linux/hash.h         | 36 ++++++++++++++++++
 lib/Makefile                 |  2 +-
 lib/hash.c                   | 38 +++++++++++++++++++
 net/openvswitch/flow_table.c |  4 +-
 8 files changed, 182 insertions(+), 4 deletions(-)
 create mode 100644 arch/x86/include/asm/hash.h
 create mode 100644 arch/x86/lib/hash.c
 create mode 100644 include/asm-generic/hash.h
 create mode 100644 lib/hash.c

-- 
1.8.3.1