-----Original Message-----
From: Vitaly Kuznetsov [mailto:vkuznets@redhat.com]
Sent: Tuesday, February 14, 2017 4:44 AM
To: x86@kernel.org; Andy Lutomirski <luto@amacapital.net>
Cc: Thomas Gleixner <redacted>; Ingo Molnar <mingo@redhat.com>;
H. Peter Anvin [off-list ref]; KY Srinivasan [off-list ref];
Haiyang Zhang [off-list ref]; Stephen Hemminger
[off-list ref]; Dexuan Cui [off-list ref]; linux-
kernel@vger.kernel.org; devel@linuxdriverproject.org;
virtualization@lists.linux-foundation.org
Subject: [PATCH v2 0/3] x86/vdso: Add Hyper-V TSC page clocksource support

Hi,

while we're still waiting for a definitive ACK from Microsoft that the algorithm
is good for SMP case (as we can't prevent the code in vdso from migrating
between CPUs) I'd like to send v2 with some modifications to keep the
discussion going.

I checked with the folks on the Hyper-V side and they have confirmed that we need to
add memory barriers in the guest code to ensure the various reads from the TSC page are
correctly ordered - especially, the initial read of the sequence counter must have acquire
semantics. We should ensure that other reads from the TSC page are completed before the
second read of the sequence counter. I am working with the Windows team to correctly
reflect this algorithm in the Hyper-V specification.

Regards,

K. Y

Changes since v1:
- Document the TSC page reading protocol [Thomas Gleixner].

- Separate the TSC page reading code from read_hv_clock_tsc() and put it to
  asm/mshyperv.h to use from both hv_init.c and vdso.

- Add explicit barriers [Thomas Gleixner]

Original description:

Hyper-V TSC page clocksource is suitable for vDSO, however, the protocol
defined by the hypervisor is different from VCLOCK_PVCLOCK. Implemented
the required support. Simple sysbench test shows the following results:

Before:
# time sysbench --test=memory --max-requests=500000 run ...
real    1m22.618s
user    0m50.193s
sys     0m32.268s

After:
# time sysbench --test=memory --max-requests=500000 run ...
real	0m47.241s
user	0m47.117s
sys	0m0.008s

Patches 1 and 2 are made on top of K. Y.'s code refactoring which moved tsc
page clocksource to arch/x86/hyperv/hv_init.c, this is currently present in
Greg's char-misc-next tree.

Vitaly Kuznetsov (3):
  x86/hyperv: implement hv_get_tsc_page()
  x86/hyperv: move TSC reading method to asm/mshyperv.h
  x86/vdso: Add VCLOCK_HVCLOCK vDSO clock read method

 arch/x86/entry/vdso/vclock_gettime.c  | 24 +++++++++++++++
arch/x86/entry/vdso/vdso-layout.lds.S |  3 +-
 arch/x86/entry/vdso/vdso2c.c          |  3 ++
 arch/x86/entry/vdso/vma.c             |  7 +++++
 arch/x86/hyperv/hv_init.c             | 48 +++++++++--------------------
 arch/x86/include/asm/clocksource.h    |  3 +-
 arch/x86/include/asm/mshyperv.h       | 58
+++++++++++++++++++++++++++++++++++
 arch/x86/include/asm/vdso.h           |  1 +
 drivers/hv/Kconfig                    |  3 ++
 9 files changed, 114 insertions(+), 36 deletions(-)

--
2.9.3