linux-kernel - Re: [PATCH] rcuwait: do not enter RCU protection unless a wakeup is needed

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Message-ID: <20211022135909.GB174703@worktop.programming.kicks-ass.net>
Date:   Fri, 22 Oct 2021 15:59:09 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Wanpeng Li <kernellwp@...il.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
        Davidlohr Bueso <dave@...olabs.net>,
        Oleg Nesterov <oleg@...hat.com>,
        Ingo Molnar <mingo@...nel.org>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        Wanpeng Li <wanpengli@...cent.com>
Subject: Re: [PATCH] rcuwait: do not enter RCU protection unless a wakeup is
 needed

On Wed, Oct 20, 2021 at 08:08:41PM +0800, Wanpeng Li wrote:
> On Wed, 20 Oct 2021 at 20:04, Paolo Bonzini <pbonzini@...hat.com> wrote:
> >
> > On 20/10/21 14:01, Wanpeng Li wrote:
> > > Yes, in the attachment.
> > >
> > >      Wanpeng
> >
> > This one does not have CONFIG_PREEMPT=y, let alone CONFIG_PREEMPT_RCU.
> > It's completely impossible that this patch has an effect without those
> > options.
> 
> Sorry, should be this one in the attachment.

Uhhmmm.. you have lockdep enabled. You know you shouldn't be doing
performance measurements with lockdep on, right?