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Subject: Re: [PATCH v2 1/4] x86/hyper-v: move synic/stimer control structures
 definitions to hyperv-tlfs.h
From:   Nadav Amit <nadav.amit@gmail.com>
In-Reply-To: <20181127184835.GA5147@rkaganip.lan>
Date:   Tue, 27 Nov 2018 17:49:29 -0800
Cc:     Vitaly Kuznetsov <vkuznets@redhat.com>,
        "K. Y. Srinivasan" <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        "Michael Kelley (EOSG)" <Michael.H.Kelley@microsoft.com>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        =?utf-8?B?UmFkaW0gS3LEjW3DocWZ?= <rkrcmar@redhat.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "x86@kernel.org" <x86@kernel.org>
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References: <20181126154732.23025-1-vkuznets@redhat.com>
 <20181126154732.23025-2-vkuznets@redhat.com>
 <20181126200413.GA7852@rkaganb.sw.ru> <87wooyk6na.fsf@vitty.brq.redhat.com>
 <20181127184835.GA5147@rkaganip.lan>
To:     Roman Kagan <rkagan@virtuozzo.com>
Sender: linux-kernel-owner@vger.kernel.org
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> On Nov 27, 2018, at 10:48 AM, Roman Kagan <rkagan@virtuozzo.com> =
wrote:
>=20
> On Tue, Nov 27, 2018 at 02:10:49PM +0100, Vitaly Kuznetsov wrote:
>> Roman Kagan <rkagan@virtuozzo.com> writes:
>>> On Mon, Nov 26, 2018 at 04:47:29PM +0100, Vitaly Kuznetsov wrote:
>>> I personally tend to prefer masks over bitfields, so I'd rather do =
the
>>> consolidation in the opposite direction: use the definitions in
>>> hyperv-tlfs.h and replace those unions/bitfields elsewhere.  (I =
vaguely
>>> remember posting such a patchset a couple of years ago but I lacked =
the
>>> motivation to complete it).
>>=20
>> Are there any known advantages of using masks over bitfields or the
>> resulting binary code is the same?
>=20
> Strictly speaking bitwise ops are portable while bitfields are not, =
but
> I guess this is not much of an issue with gcc which is dependable to
> produce the right thing.
>=20
> I came to dislike the bitfields for the false feeling of atomicity of
> assignment while most of the time they are read-modify-write =
operations.
>=20
> And no, I don't feel strong about it, so if nobody backs me on this I
> give up :)

Last time I tried to push a change from bitmasks to bitfields I failed:
https://lkml.org/lkml/2014/9/16/245

On a different note: how come all of the hyper-v structs are not marked
with the =E2=80=9Cpacked" attribute?=