Re: [PATCH V7 0/2] KSM replace hash algo with xxhash

[Pasha Tatashin <Pavel.Tatashin@microsoft.com>]

On 9/13/18 5:19 PM, Timofey Titovets wrote:
> From: Timofey Titovets <nefelim4ag@gmail.com>
> 
> Currently used jhash are slow enough and replace it allow as to make KSM
> less cpu hungry.
> 
> About 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
> 
> By sioh Lee tests (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:
>   - Fisrt patch implement compile time pickup of fastest implementation of xxhash
>     for target platform.
>   - Second replace jhash2 with xxhash
>   
> Thanks.
> 
> CC: Andrea Arcangeli <aarcange@redhat.com>
> CC: linux-mm@kvack.org
> CC: kvm@vger.kernel.org
> CC: leesioh <solee@os.korea.ac.kr>
> 
> Timofey Titovets (2):
>   xxHash: create arch dependent 32/64-bit xxhash()
>   ksm: replace jhash2 with xxhash
> 
>  include/linux/xxhash.h | 23 +++++++++++++
>  mm/Kconfig             |  2 ++
>  mm/ksm.c               | 93 +++++++++++++++++++++++++++++++++++++++++++++++---
>  3 files changed, 114 insertions(+), 4 deletions(-)

This is wrong stat. ksm.c should not have any new lines at all.