linux-kernel - [PATCH v4 0/2] reduce TSC deadline frequency errors

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Date:	Thu, 14 Jul 2016 17:22:53 +0200
From:	Nicolai Stange <nicstange@...il.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>,
	x86@...nel.org, Borislav Petkov <bp@...e.de>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Hidehiro Kawai <hidehiro.kawai.ez@...achi.com>,
	"Peter Zijlstra (Intel)" <peterz@...radead.org>,
	"Christopher S. Hall" <christopher.s.hall@...el.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	linux-kernel@...r.kernel.org, Nicolai Stange <nicstange@...il.com>
Subject: [PATCH v4 0/2] reduce TSC deadline frequency errors

The v3 series can be found at

  http://lkml.kernel.org/g/20160713130344.8319-1-nicstange@gmail.com

Applicable to linux-next-20160708 (in case you wonder why I turned back
from the 20160712 given in v3 to 20160708 again: mysteriously, 20160712
doesn't boot neither w/ nor w/o this series anymore).

The individual patches don't depend on each other.

Changes to v3:
  As Paolo Bonzini pointed out in reply to v3, for the values of 2, 4 and
  8 of TSC_DIVISOR, the 64 bit division
    (u32)(((u64)tsc_khz * 1000) / TSC_DIVISOR)
  can be safely turned into a 32 bit division by changing associativity:
    tsc_khz * (1000 / TSC_DIVISOR)

  In doing so, it suggests itself to squash former [1/3] ("arch, x86, tsc
  deadline clockevent dev: reduce frequency roundoff error") and
  [2/3] ("arch, x86, tsc deadline clockevent dev: reduce TSC_DIVISOR to 2")
  into a single patch. Furthermore, reducing TSC_DIVISOR down to 2 becomes
  unnessecary -- setting it to 8 suffices already.

  Thus,
  - [1/2] ("arch, x86, tsc deadline clockevent dev: eliminate frequency
            roundoff error")
      Former [1/3] and [2/3] squashed together. Don't reduce TSC_DIVISOR
      to 2 but to 8 only. Change associativity in order to get rid of the
      64 bit division. Adapt the commit message accordingly.
  - [2/2] ("arch, x86, tsc: inform TSC deadline clockevent device about
            recalibration")
      Former [3/3]. Likewise change associativity in order to get rid of
      the 64 bit division here, too.

Changes to v2:
  - [3/3] ("arch, x86, tsc: inform TSC deadline clockevent device about
            recalibration")
      Use clockevents_update_freq() rather than clockevents_config().

  - Former [4/4] ("kernel/time/clockevents: compensate for monotonic
                   clock's dynamic frequency")
      Split off, not a member of this series anymore.

Changes to v1:
  - [1/3] ("arch, x86, tsc deadline clockevent dev: reduce frequency
            roundoff error")
      No changes to the patch. Note that the v1 mail could not be delivered
      to the author of the TSC_DIVISOR introducing commit 279f1461432c
      ("x86: apic: Use tsc deadline for oneshot when available"),
      Suresh Siddha <suresh.b.siddha@...el.com>, so I had to remove him
      from the CC list.

  - [2/3] ("arch, x86, tsc deadline clockevent dev: reduce TSC_DIVISOR
            to 2")
      Likewise.

  - [3/3] ("arch, x86, tsc: inform TSC deadline clockevent device about
            recalibration")
      Silence the kbuild test robot on ARCH=i386 by wrapping the new call
      to lapic_update_tsc_freq() from arch/x86/kernel/tsc.c in an
      #ifdef CONFIG_X86_LOCAL_APIC.

Nicolai Stange (2):
  arch, x86, tsc deadline clockevent dev: eliminate frequency roundoff
    error
  arch, x86, tsc: inform TSC deadline clockevent device about
    recalibration

 arch/x86/include/asm/apic.h |  1 +
 arch/x86/kernel/apic/apic.c | 28 ++++++++++++++++++++++++++--
 arch/x86/kernel/tsc.c       |  6 ++++++
 3 files changed, 33 insertions(+), 2 deletions(-)

-- 
2.9.0