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Date:   Wed, 9 Oct 2019 11:32:10 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Paolo Bonzini <pbonzini@redhat.com>
Cc:     Like Xu <like.xu@linux.intel.com>, kvm@vger.kernel.org,
        rkrcmar@redhat.com, sean.j.christopherson@intel.com,
        vkuznets@redhat.com, Jim Mattson <jmattson@google.com>,
        Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        ak@linux.intel.com, wei.w.wang@intel.com, kan.liang@intel.com,
        like.xu@intel.com, ehankland@google.com, arbel.moshe@oracle.com,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 3/3] KVM: x86/vPMU: Add lazy mechanism to release
 perf_event per vPMC
Message-ID: <20191009093210.GK2328@hirez.programming.kicks-ass.net>
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On Wed, Oct 09, 2019 at 11:21:30AM +0200, Paolo Bonzini wrote:
> On 09/10/19 10:16, Peter Zijlstra wrote:

> >> bool bitfields preserve the magic behavior where something like this:
> >>
> >>   foo->x = y;
> >>
> >> (x is a bool bitfield) would be compiled as
> >>
> >>   foo->x = (y != 0);
> > 
> > This is confusion; if y is a single bit bitfield, then there is
> > absolutely _NO_ difference between these two expressions.
> 
> y is not in a struct so it cannot be a single bit bitfield. :) If y is
> an int and foo->x is a bool bitfield, you get the following:
> 
> 	foo->x = 6;	/* foo->x is 1, it would be 0 for int:1 */
> 	foo->x = 7;	/* foo->x is 1, it would be 1 for int:1 */
> 

Urgh, reading hard. You're right!