linux-kernel - Re: [PATCH V2 7/7] x86,rcu: use percpu rcu_preempt

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Date:   Sun, 3 Nov 2019 12:33:16 +0800
From:   Lai Jiangshan <laijs@...ux.alibaba.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Josh Triplett <josh@...htriplett.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Kees Cook <keescook@...omium.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Dave Hansen <dave.hansen@...el.com>,
        Babu Moger <Babu.Moger@....com>,
        Rik van Riel <riel@...riel.com>,
        "Chang S. Bae" <chang.seok.bae@...el.com>,
        Jann Horn <jannh@...gle.com>,
        David Windsor <dwindsor@...il.com>,
        Elena Reshetova <elena.reshetova@...el.com>,
        Yuyang Du <duyuyang@...il.com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Richard Guy Briggs <rgb@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Michal Hocko <mhocko@...e.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        "Dmitry V. Levin" <ldv@...linux.org>, rcu@...r.kernel.org
Subject: Re: [PATCH V2 7/7] x86,rcu: use percpu rcu_preempt_depth



On 2019/11/3 12:30 上午, Borislav Petkov wrote:
> Resending again because your mail has the craziest header:
> 
> Reply-To: 20191101162109.GN20975@...lmck-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@...radead.org>
>> Signed-off-by: Lai Jiangshan <laijs@...ux.alibaba.com>
>> ---
>>   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.