Re: [PATCH V2 7/7] x86,rcu: use percpu rcu_preempt_depth

[Lai Jiangshan]

On 2019/11/3 12:30 äå, Borislav Petkov wrote:
> Resending again because your mail has the craziest header:
>
> Reply-To: 20191101162109.GN20975@paulmck-ThinkPad-P72
>
> and hitting Reply-to-all creates only confusion. WTF?


Sorry, I send the emails via git send-email with the wrong
argument "--reply-to", it should have been "--in-reply-to".

> On Sat, Nov 02, 2019 at 12:45:59PM +0000, Lai Jiangshan wrote:
> > Convert x86 to use a per-cpu rcu_preempt_depth. The reason for doing so
> > is that accessing per-cpu variables is a lot cheaper than accessing
> > task_struct or thread_info variables.
> >
> > We need to save/restore the actual rcu_preempt_depth when switch.
> > We also place the per-cpu rcu_preempt_depth close to __preempt_count
> > and current_task variable.
> >
> > Using the idea of per-cpu __preempt_count.
> >
> > No function call when using rcu_read_[un]lock().
> > Single instruction for rcu_read_lock().
> > 2 instructions for fast path of rcu_read_unlock().
> >
> > CC: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > Signed-off-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxxxxx>
> > ---
> >   arch/x86/Kconfig                         |  2 +
> >   arch/x86/include/asm/rcu_preempt_depth.h | 87 ++++++++++++++++++++++++
> >   arch/x86/kernel/cpu/common.c             |  7 ++
> >   arch/x86/kernel/process_32.c             |  2 +
> >   arch/x86/kernel/process_64.c             |  2 +
> >   include/linux/rcupdate.h                 | 24 +++++++
> >   init/init_task.c                         |  2 +-
> >   kernel/fork.c                            |  2 +-
> >   kernel/rcu/Kconfig                       |  3 +
> >   kernel/rcu/tree_exp.h                    |  2 +
> >   kernel/rcu/tree_plugin.h                 | 37 +++++++---
> >   11 files changed, 158 insertions(+), 12 deletions(-)
> >   create mode 100644 arch/x86/include/asm/rcu_preempt_depth.h
> >
> > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> > index d6e1faa28c58..af9fedc0fdc4 100644
> > --- a/arch/x86/Kconfig
> > +++ b/arch/x86/Kconfig
> > @@ -18,6 +18,7 @@ config X86_32
> >   	select MODULES_USE_ELF_REL
> >   	select OLD_SIGACTION
> >   	select GENERIC_VDSO_32
> > +	select ARCH_HAVE_RCU_PREEMPT_DEEPTH
>
> WTF is a "DEEPTH"?

Sorry, bad English.