[Devel] [PATCH RH8 06/10] ms/xxHash: create arch dependent 32/64-bit xxhash()

[Andrey Zhadchenko]

From: Timofey Titovets <nefelim4ag at gmail.com>

Patch series "Currently used jhash are slow enough and replace it allow as
to make KSM", v8.

Speed (in kernel):
	ksm: crc32c   hash() 12081 MB/s
	ksm: xxh64    hash()  8770 MB/s
	ksm: xxh32    hash()  4529 MB/s
	ksm: jhash2   hash()  1569 MB/s

Sioh Lee's testing (copy from other mail):

Test platform: openstack cloud platform (NEWTON version)
Experiment node: openstack based cloud compute node (CPU: xeon E5-2620 v3, memory 64gb)
VM: (2 VCPU, RAM 4GB, DISK 20GB) * 4
Linux kernel: 4.14 (latest version)
KSM setup - sleep_millisecs: 200ms, pages_to_scan: 200

Experiment process:
Firstly, we turn off KSM and launch 4 VMs.  Then we turn on the KSM and
measure the checksum computation time until full_scans become two.

The experimental results (the experimental value is the average of the measured values)
crc32c_intel: 1084.10ns
crc32c (no hardware acceleration): 7012.51ns
xxhash32: 2227.75ns
xxhash64: 1413.16ns
jhash2: 5128.30ns

In summary, the result shows that crc32c_intel has advantages over all of
the hash function used in the experiment.  (decreased by 84.54% compared
to crc32c, 78.86% compared to jhash2, 51.33% xxhash32, 23.28% compared to
xxhash64) the results are similar to those of Timofey.

But, use only xxhash for now, because for using crc32c, cryptoapi must be
initialized first - that require some tricky solution to work good in all
situations.

So:

- First patch implement compile time pickup of fastest implementation of
  xxhash for target platform.

- The second patch replaces jhash2 with xxhash

This patch (of 2):

xxh32() - fast on both 32/64-bit platforms
xxh64() - fast only on 64-bit platform

Create xxhash() which will pick up the fastest version at compile time.

Link: http://lkml.kernel.org/r/20181023182554.23464-2-nefelim4ag@gmail.com
Signed-off-by: Timofey Titovets <nefelim4ag at gmail.com>
Reviewed-by: Pavel Tatashin <pavel.tatashin at microsoft.com>
Reviewed-by: Mike Rapoport <rppt at linux.vnet.ibm.com>
Reviewed-by: Andrew Morton <akpm at linux-foundation.org>
Cc: Andrea Arcangeli <aarcange at redhat.com>
Cc: leesioh <solee at os.korea.ac.kr>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>

=====================
Patchset description:

ksm: Switch to xxhash hash algorithm

xxhash shows better performance in comparison to currently
used jhash2:

        ksm: xxh64 hash() 8770 MB/s
        ksm: xxh32 hash() 4529 MB/s
        ksm: jhash2 hash() 1569 MB/s

Note, that algorithm module lib/xxhash.c is already in ms kernel [1/3],
while [2-3/3] just make ksm to use it (but they also already in akpm tree).

This should improve ksm performance in some way.

Nick Terrell (1):
      lib: Add xxhash module

Timofey Titovets (2):
      xxHash: create arch dependent 32/64-bit xxhash()
      ksm: replace jhash2 with xxhash

https://jira.sw.ru/browse/PSBM-90044

(cherry-picked from 4d54c1ca1c908f02912f9d8ae2bc6d18ba8c2237)
Signed-off-by: Andrey Zhadchenko <andrey.zhadchenko at virtuozzo.com>

diff --git a/include/linux/xxhash.h b/include/linux/xxhash.h
index 9e1f42c..52b073f 100644
--- a/include/linux/xxhash.h
+++ b/include/linux/xxhash.h
@@ -107,6 +107,29 @@
  */
 uint64_t xxh64(const void *input, size_t length, uint64_t seed);
 
+/**
+ * xxhash() - calculate wordsize hash of the input with a given seed
+ * @input:  The data to hash.
+ * @length: The length of the data to hash.
+ * @seed:   The seed can be used to alter the result predictably.
+ *
+ * If the hash does not need to be comparable between machines with
+ * different word sizes, this function will call whichever of xxh32()
+ * or xxh64() is faster.
+ *
+ * Return:  wordsize hash of the data.
+ */
+
+static inline unsigned long xxhash(const void *input, size_t length,
+				   uint64_t seed)
+{
+#if BITS_PER_LONG == 64
+       return xxh64(input, length, seed);
+#else
+       return xxh32(input, length, seed);
+#endif
+}
+
 /*-****************************
  * Streaming Hash Functions
  *****************************/
-- 
1.8.3.1