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

[Timofey Titovets <timofey.titovets@synesis.ru>]

пт, 14 сент. 2018 г. в 0:26, 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.

Sorry, just copy-paste error when i rework patchset.
Must be:
 include/linux/xxhash.h | 23 +++++++++++++++++++++++
 mm/Kconfig             |  1 +
 mm/ksm.c               |  4 ++--

And i leave some useless new lines in second patch, i can drop them
byself and resend if that needed.

Thanks.