Re: [PATCH] x86/hyper-v: enable TSC page clocksource on 32bit

On Wed, 21 Aug 2019, Thomas Gleixner wrote:

On Wed, 21 Aug 2019, Vitaly Kuznetsov wrote:

quoted

There is no particular reason to not enable TSC page clocksource
on 32-bit. mul_u64_u64_shr() is available and despite the increased
computational complexity (compared to 64bit) TSC page is still a huge
win compared to MSR-based clocksource.

In-kernel reads:
  MSR based clocksource: 3361 cycles
  TSC page clocksource: 49 cycles

Reads from userspace (unilizing vDSO in case of TSC page):
  MSR based clocksource: 5664 cycles
  TSC page clocksource: 131 cycles

Enabling TSC page on 32bits allows us to get rid of CONFIG_HYPERV_TSCPAGE

s/allows us/allows/

quoted

as it is now not any different from CONFIG_HYPERV_TIMER.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
 arch/x86/include/asm/vdso/gettimeofday.h |  6 +++---
 drivers/clocksource/hyperv_timer.c       | 11 -----------
 drivers/hv/Kconfig                       |  3 ---
 include/clocksource/hyperv_timer.h       |  6 ++----
 4 files changed, 5 insertions(+), 21 deletions(-)

Really nice cleanup as a side effect of adding functionality.

That said, could you please rebase that on

  git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git timers/core

as I just applied the TSC page patches there and this conflicts left and
right.

Thanks,

	tglx