linux-toradex.git/arch/x86/include/asm/pvclock.h, branch v4.2.7

x86: kvmclock: drop rdtsc_barrier()

2015-05-07T09:29:48+00:00

Drop unnecessary rdtsc_barrier(), as has been determined empirically,
see 057e6a8c660e95c3f4e7162e00e2fee1fc90c50d for details.

Noticed by Andy Lutomirski.

Improves clock_gettime() by approximately 15% on
Intel i7-3520M @ 2.90GHz.

Signed-off-by: Marcelo Tosatti 
Signed-off-by: Paolo Bonzini

x86: pvclock: Really remove the sched notifier for cross-cpu migrations

2015-04-27T13:49:30+00:00

This reverts commits 0a4e6be9ca17c54817cf814b4b5aa60478c6df27
and 80f7fdb1c7f0f9266421f823964fd1962681f6ce.

The task migration notifier was originally introduced in order to support
the pvclock vsyscall with non-synchronized TSC, but KVM only supports it
with synchronized TSC.  Hence, on KVM the race condition is only needed
due to a bad implementation on the host side, and even then it's so rare
that it's mostly theoretical.

As far as KVM is concerned it's possible to fix the host, avoiding the
additional complexity in the vDSO and the (re)introduction of the task
migration notifier.

Xen, on the other hand, hasn't yet implemented vsyscall support at
all, so we do not care about its plans for non-synchronized TSC.

Reported-by: Peter Zijlstra 
Suggested-by: Marcelo Tosatti 
Signed-off-by: Paolo Bonzini

x86: kvm: Revert "remove sched notifier for cross-cpu migrations"

2015-03-23T23:22:48+00:00

The following point:

    2. per-CPU pvclock time info is updated if the
       underlying CPU changes.

Is not true anymore since "KVM: x86: update pvclock area conditionally,
on cpu migration".

Add task migration notification back.

Problem noticed by Andy Lutomirski.

Signed-off-by: Marcelo Tosatti 
CC: stable@kernel.org # 3.11+

pvclock: detect watchdog reset at pvclock read

2013-11-06T07:48:43+00:00

Implement reset of kernel watchdogs at pvclock read time. This avoids
adding special code to every watchdog.

This is possible for watchdogs which measure time based on sched_clock() or
ktime_get() variants.

Suggested by Don Zickus.

Acked-by: Don Zickus 
Acked-by: Paolo Bonzini 
Signed-off-by: Marcelo Tosatti 
Signed-off-by: Gleb Natapov

remove sched notifier for cross-cpu migrations

2013-07-18T10:29:30+00:00

Linux as a guest on KVM hypervisor, the only user of the pvclock
vsyscall interface, does not require notification on task migration
because:

1. cpu ID number maps 1:1 to per-CPU pvclock time info.
2. per-CPU pvclock time info is updated if the
   underlying CPU changes.
3. that version is increased whenever underlying CPU
   changes.

Which is sufficient to guarantee nanoseconds counter
is calculated properly.

Signed-off-by: Marcelo Tosatti 
Acked-by: Peter Zijlstra 
Signed-off-by: Gleb Natapov

x86: pvclock: generic pvclock vsyscall initialization

2012-11-28T01:29:09+00:00

Originally from Jeremy Fitzhardinge.

Introduce generic, non hypervisor specific, pvclock initialization
routines.

Signed-off-by: Marcelo Tosatti

x86: pvclock: add note about rdtsc barriers

2012-11-28T01:29:08+00:00

As noted by Gleb, not advertising SSE2 support implies
no RDTSC barriers.

Signed-off-by: Marcelo Tosatti

x86: pvclock: introduce helper to read flags

2012-11-28T01:29:08+00:00

Acked-by: Glauber Costa 
Signed-off-by: Marcelo Tosatti

x86: pvclock: create helper for pvclock data retrieval

2012-11-28T01:29:07+00:00

Originally from Jeremy Fitzhardinge.

So code can be reused.

Acked-by: Glauber Costa 
Signed-off-by: Marcelo Tosatti

KVM: Fix instruction size issue in pvclock scaling

2011-08-30T11:42:30+00:00

Commit de2d1a524e94 ("KVM: Fix register corruption in pvclock_scale_delta")
introduced a mul instruction that may have only a memory operand; the
assembler therefore cannot select the correct size:

   pvclock.s:229: Error: no instruction mnemonic suffix given and no register
operands; can't size instruction

In this example the assembler is:

         #APP
         mul -48(%rbp) ; shrd $32, %rdx, %rax
         #NO_APP

A simple solution is to use mulq.

Signed-off-by: Duncan Sands 
Signed-off-by: Avi Kivity