linux-kernel - Re: [PATCH 1/3] context_tracking: New context tracking susbsystem

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Date:	Tue, 6 Nov 2012 11:53:53 +0200
From:	Gilad Ben-Yossef <gilad@...yossef.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 1/3] context_tracking: New context tracking susbsystem

On Sat, Nov 3, 2012 at 6:09 PM, Frederic Weisbecker <fweisbec@...il.com> wrote:
> 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.
> ...
>
> diff --git a/arch/Kconfig b/arch/Kconfig
> index 366ec06..3855e06 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -300,15 +300,15 @@ config SECCOMP_FILTER
>
>           See Documentation/prctl/seccomp_filter.txt for details.
>
> -config HAVE_RCU_USER_QS
> +config HAVE_CONTEXT_TRACKING
>         bool
>         help
> -         Provide kernel entry/exit hooks necessary for userspace
> +         Provide kernel/user boundaries probes necessary for userspace
>           RCU extended quiescent state. Syscalls need to be wrapped inside

A minor nit pick: if whole point of the patch is to turn an RCU
specific mechanism to a generic one
that RCU happens to use, then the text needs to reflect that. How about:

"Provide kernel/user boundaries probes necessary for subsystems that
need it, such as userspace
RCU extended quiescent state. "


> -         rcu_user_exit()-rcu_user_enter() through the slow path using
> -         TIF_NOHZ flag. Exceptions handlers must be wrapped as well. Irqs
> -         are already protected inside rcu_irq_enter/rcu_irq_exit() but
> -         preemption or signal handling on irq exit still need to be protected.
> +         user_exit()-user_enter() through the slow path using TIF_NOHZ flag.
> +         Exceptions handlers must be wrapped as well. Irqs are already
> +         protected inside rcu_irq_enter/rcu_irq_exit() but preemption or
> +         signal handling on irq exit still need to be protected.
>

Thanks,
Gilad

-- 
Gilad Ben-Yossef
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gilad@...yossef.com
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