14 Aug, 2013
6 commits
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If no CPU is in the full dynticks range, we can avoid the full
dynticks cputime accounting through generic vtime along with its
overhead and use the traditional tick based accounting instead.Let's do this and nope the off case with static keys.
Signed-off-by: Frederic Weisbecker
Cc: Steven Rostedt
Cc: Paul E. McKenney
Cc: Ingo Molnar
Cc: Thomas Gleixner
Cc: Peter Zijlstra
Cc: Borislav Petkov
Cc: Li Zhong
Cc: Mike Galbraith
Cc: Kevin Hilman -
We plan to use the context tracking static key on inline
vtime APIs. For this we need to include the context tracking
headers from those of vtime.However vtime headers need to stay low level because they are
included in hardirq.h that mostly contains standalone
definitions. But context_tracking.h includes sched.h for
a few task_struct references, therefore it wouldn't be sensible
to include it from vtime.hTo solve this, lets split the context tracking headers and move
out the pure state definitions that only require a few low level
headers. We can safely include that small part in vtime.h later.Signed-off-by: Frederic Weisbecker
Cc: Steven Rostedt
Cc: Paul E. McKenney
Cc: Ingo Molnar
Cc: Thomas Gleixner
Cc: Peter Zijlstra
Cc: Borislav Petkov
Cc: Li Zhong
Cc: Mike Galbraith
Cc: Kevin Hilman -
No need for syscall slowpath if no CPU is full dynticks,
rather nop this in this case.Signed-off-by: Frederic Weisbecker
Cc: Steven Rostedt
Cc: Paul E. McKenney
Cc: Ingo Molnar
Cc: Thomas Gleixner
Cc: Peter Zijlstra
Cc: Borislav Petkov
Cc: Li Zhong
Cc: Mike Galbraith
Cc: Kevin Hilman -
Optimize guest entry/exit APIs with static keys. This minimize
the overhead for those who enable CONFIG_NO_HZ_FULL without
always using it. Having no range passed to nohz_full= should
result in the probes overhead to be minimized.Signed-off-by: Frederic Weisbecker
Cc: Steven Rostedt
Cc: Paul E. McKenney
Cc: Ingo Molnar
Cc: Thomas Gleixner
Cc: Peter Zijlstra
Cc: Borislav Petkov
Cc: Li Zhong
Cc: Mike Galbraith
Cc: Kevin Hilman -
Optimize user and exception entry/exit APIs with static
keys. This minimize the overhead for those who enable
CONFIG_NO_HZ_FULL without always using it. Having no range
passed to nohz_full= should result in the probes to be nopped
(at least we hope so...).If this proves not be enough in the long term, we'll need
to bring an exception slow path by re-routing the exception
handlers.Signed-off-by: Frederic Weisbecker
Cc: Steven Rostedt
Cc: Paul E. McKenney
Cc: Ingo Molnar
Cc: Thomas Gleixner
Cc: Peter Zijlstra
Cc: Borislav Petkov
Cc: Li Zhong
Cc: Mike Galbraith
Cc: Kevin Hilman -
Prepare for using a static key in the context tracking subsystem.
This will help optimizing the off case on its many users:* user_enter, user_exit, exception_enter, exception_exit, guest_enter,
guest_exit, vtime_*()Signed-off-by: Frederic Weisbecker
Cc: Steven Rostedt
Cc: Paul E. McKenney
Cc: Ingo Molnar
Cc: Thomas Gleixner
Cc: Peter Zijlstra
Cc: Borislav Petkov
Cc: Li Zhong
Cc: Mike Galbraith
Cc: Kevin Hilman
13 Aug, 2013
3 commits
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The context tracking subsystem has the ability to selectively
enable the tracking on any defined subset of CPU. This means that
we can define a CPU range that doesn't run the context tracking
and another range that does.Now what we want in practice is to enable the tracking on full
dynticks CPUs only. In order to perform this, we just need to pass
our full dynticks CPU range selection from the full dynticks
subsystem to the context tracking.This way we can spare the overhead of RCU user extended quiescent
state and vtime maintainance on the CPUs that are outside the
full dynticks range. Just keep in mind the raw context tracking
itself is still necessary everywhere.Signed-off-by: Frederic Weisbecker
Cc: Steven Rostedt
Cc: Paul E. McKenney
Cc: Ingo Molnar
Cc: Thomas Gleixner
Cc: Peter Zijlstra
Cc: Borislav Petkov
Cc: Li Zhong
Cc: Mike Galbraith
Cc: Kevin Hilman -
Update a stale comment from the old vtime era and document some
locking that might be non obvious.Signed-off-by: Frederic Weisbecker
Cc: Steven Rostedt
Cc: Paul E. McKenney
Cc: Ingo Molnar
Cc: Thomas Gleixner
Cc: Peter Zijlstra
Cc: Borislav Petkov
Cc: Li Zhong
Cc: Mike Galbraith
Cc: Kevin Hilman -
1) If context tracking is enabled with native vtime accounting (which
combo is useless except for dev testing), we call vtime_guest_enter()
and vtime_guest_exit() on host guest switches. But those are stubs
in this configurations. As a result, cputime is not correctly flushed
on kvm context switches.2) If context tracking runs but is disabled on some CPUs, those
CPUs end up calling __guest_enter/__guest_exit which in turn
call vtime_account_system(). We don't want to call this because we
run in tick based accounting for these CPUs.Refactor the guest_enter/guest_exit code such that all combinations
finally work.Signed-off-by: Frederic Weisbecker
Cc: Steven Rostedt
Cc: Paul E. McKenney
Cc: Ingo Molnar
Cc: Thomas Gleixner
Cc: Peter Zijlstra
Cc: Borislav Petkov
Cc: Li Zhong
Cc: Mike Galbraith
Cc: Kevin Hilman
31 May, 2013
1 commit
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The kvm_host.h header file doesn't handle well
inclusion when archs don't support KVM.This results in build crashes for such archs when they
want to implement context tracking because this subsystem
includes kvm_host.h in order to implement the
guest_enter/exit APIs but it doesn't handle KVM off case.To fix this, move the guest_enter()/guest_exit()
declarations and generic implementation to the context
tracking headers. These generic APIs actually belong to
this subsystem, besides other domains boundary tracking
like user_enter() et al.KVM now properly becomes a user of this library, not the
other buggy way around.Reported-by: Kevin Hilman
Reviewed-by: Kevin Hilman
Tested-by: Kevin Hilman
Signed-off-by: Frederic Weisbecker
Cc: Steven Rostedt
Cc: Paul E. McKenney
Cc: Thomas Gleixner
Cc: Peter Zijlstra
Cc: Kevin Hilman
Cc: Marcelo Tosatti
Cc: Gleb Natapov
Signed-off-by: Ingo Molnar
08 Mar, 2013
2 commits
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On exception exit, we restore the previous context tracking state based on
the regs of the interrupted frame. Iff that frame is in user mode as
stated by user_mode() helper, we restore the context tracking user mode.However there is a tiny chunck of low level arch code after we pass through
user_enter() and until the CPU eventually resumes userspace.
If an exception happens in this tiny area, exception_enter() correctly
exits the context tracking user mode but exception_exit() won't restore
it because of the value returned by user_mode(regs).As a result we may return to userspace with the wrong context tracking
state.To fix this, change exception_enter() to return the context tracking state
prior to its call and pass this saved state to exception_exit(). This restores
the real context tracking state of the interrupted frame.(May be this patch was suggested to me, I don't recall exactly. If so,
sorry for the missing credit).Signed-off-by: Frederic Weisbecker
Cc: Li Zhong
Cc: Kevin Hilman
Cc: Mats Liljegren
Cc: Peter Zijlstra
Cc: Ingo Molnar
Cc: Steven Rostedt
Cc: Namhyung Kim
Cc: Andrew Morton
Cc: Thomas Gleixner
Cc: Paul E. McKenney -
Exceptions handling on context tracking should share common
treatment: on entry we exit user mode if the exception triggered
in that context. Then on exception exit we return to that previous
context.Generalize this to avoid duplication across archs.
Signed-off-by: Frederic Weisbecker
Cc: Li Zhong
Cc: Kevin Hilman
Cc: Mats Liljegren
Cc: Peter Zijlstra
Cc: Ingo Molnar
Cc: Steven Rostedt
Cc: Namhyung Kim
Cc: Andrew Morton
Cc: Thomas Gleixner
Cc: Paul E. McKenney
27 Jan, 2013
1 commit
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Export the context state: whether we run in user / kernel
from the context tracking subsystem point of view.This is going to be used by the generic virtual cputime
accounting subsystem that is needed to implement the full
dynticks.Signed-off-by: Frederic Weisbecker
Cc: Andrew Morton
Cc: Ingo Molnar
Cc: Li Zhong
Cc: Namhyung Kim
Cc: Paul E. McKenney
Cc: Paul Gortmaker
Cc: Peter Zijlstra
Cc: Steven Rostedt
Cc: Thomas Gleixner
01 Dec, 2012
1 commit
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Create a new subsystem that probes on kernel boundaries
to keep track of the transitions between level contexts
with two basic initial contexts: user or kernel.This is an abstraction of some RCU code that use such tracking
to implement its userspace extended quiescent state.We need to pull this up from RCU into this new level of indirection
because this tracking is also going to be used to implement an "on
demand" generic virtual cputime accounting. A necessary step to
shutdown the tick while still accounting the cputime.Signed-off-by: Frederic Weisbecker
Cc: Andrew Morton
Cc: H. Peter Anvin
Cc: Ingo Molnar
Cc: Paul E. McKenney
Cc: Peter Zijlstra
Cc: Steven Rostedt
Cc: Thomas Gleixner
Cc: Li Zhong
Cc: Gilad Ben-Yossef
Reviewed-by: Steven Rostedt
[ paulmck: fix whitespace error and email address. ]
Signed-off-by: Paul E. McKenney