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Subject: Re: [PATCH] x86: Align TLB invalidation info
From:   Nadav Amit <nadav.amit@gmail.com>
In-Reply-To: <BD28D2CF-CAD7-45A1-87D0-DE38F7B0EFE5@amacapital.net>
Date:   Wed, 31 Jan 2018 12:48:14 -0800
Cc:     x86@kernel.org, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, linux-kernel@vger.kernel.org,
        Peter Zijlstra <peterz@infradead.org>,
        Andy Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>
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Message-Id: <747E60F0-2315-4BEC-895E-0E29C57A0AF0@gmail.com>
References: <20180131201118.1694-1-namit@vmware.com>
 <BD28D2CF-CAD7-45A1-87D0-DE38F7B0EFE5@amacapital.net>
To:     Andy Lutomirski <luto@amacapital.net>
Sender: linux-kernel-owner@vger.kernel.org
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Andy Lutomirski <luto@amacapital.net> wrote:

>=20
>=20
>> On Jan 31, 2018, at 12:11 PM, Nadav Amit <namit@vmware.com> wrote:
>>=20
>> The TLB invalidation info is allocated on the stack, which might =
cause
>> it to be unaligned. Since this information may be transferred to
>> different cores for TLB shootdown, this might result in an additional
>> cache-line bouncing between the cores.
>>=20
>> GCC provides a way to deal with it by using
>> __builtin_alloca_with_align(). Use it to avoid the bouncing cache =
lines.
>=20
> Eww.  How about __aligned?

Err.. Stupid me. For some reason I remembered I tried it and it didn=E2=80=
=99t have
the desired effect, which caused me to assume it does not work for =
variables
on the stack. Anyhow, it does the work. I=E2=80=99ll submit v2.