linux-kernel - Re:Re: [PATCH,RESEND] softirq: Introduce SOFTIRQ_FORCED

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <AJ*AdQAQD9tzCOr4iYm-E4pL.3.1630117097688.Hmail.wangqing@vivo.com>
Date:   Sat, 28 Aug 2021 10:18:17 +0800 (GMT+08:00)
From:   王擎 <wangqing@...o.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Michal Hocko <mhocko@...nel.org>,
        Davidlohr Bueso <dave@...olabs.net>,
        Will Deacon <will@...nel.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Dirk Behme <dirk.behme@...bosch.com>,
        linux-kernel@...r.kernel.org
Subject: Re:Re: [PATCH,RESEND] softirq: Introduce SOFTIRQ_FORCED_THREADING


>Wang,
>
>On Mon, Aug 23 2021 at 11:33, Wang Qing wrote:
>
>> At present, whether the softirq is executed when the interrupt exits 
>> is controlled by IRQ_FORCED_THREADING. This is unreasonable. It should 
>> be split and allowed to take effect separately.
>
>There is nothing unreasonable about it. When interrupt force threading
>is in effect then it obviously requires that soft interrupt processing
>goes into threaded mode as well. But the threaded execution still takes
>place when the force threaded interrupt handler completes. Only softirqs
>which are raised from hard interrupt context (e.g. timer interrupt) are
>forced off to ksoftirqd.
>
>What you are proposing here is completly different as you enforce
>softirq execution in context of ksoftirqd only.

Thank you for reply and explanation, I just provide a choice to balance
the execution of softirq according to their own business scenarios.

>
>> At the same time, we should increase the priority of ksoftirqd when
>> forbidden to execute in interrupt exits. I refer to the implementation 
>> of PREEMPT_RT and think it is reasonable.
>
>What are you referring to? PREEMPT_RT does not modify the priority of
>ksoftirqd. If system designers want to do that, then they can do so from
>user space. 

I refer to the kernel-3.14 RT Patches. I used it at that time and achieved 
very good results.
I remember where I saw that softirqd was split into the original process 
and the RT process. This can partially solve my problem.

>
>And doing so can be problematic depending on the workload as this
>effectively breaks the softirq overload mitigation mechanism which
>depends on deferring to ksoftirqd so that e.g. the consumers of received
>network packets can be scheduled and the system can make progress.
>
>Just because it does not break on your system with your particular
>workload and configuration does not make it suitable for general
>consumption.
>
>> +#ifdef CONFIG_SOFTIRQ_FORCED_THREADING
>> +static inline void invoke_softirq(void)
>> +{
>> +	wakeup_softirqd();
>
>Depending on the configuration and timing this breaks any early boot
>mechanism which depends on softirqs being handled before ksoftirqd is
>available. This was clearly never tested with full RCU debugging
>enabled. 
>
>Aside of that the changelog lacks any form of technical analysis and
>justification for this. Just claiming that things are [un]reasonable and
>making uninformed statements about PREEMPT_RT does not qualify. Quite
>the contrary it's definitely unreasonable.
>
>Thanks,
>
>        tglx
>
>

Thank you for your patient guidance, if necessary, I will add it in the next version.

Thanks,
Qing