Re: [PATCH] x86: Align TLB invalidation info

[Andy Lutomirski]

On Wed, Jan 31, 2018 at 12:48 PM, Nadav Amit <nadav.amit@xxxxxxxxx> wrote:
> Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
>
>>
>>
>>> On Jan 31, 2018, at 12:11 PM, Nadav Amit <namit@xxxxxxxxxx> wrote:
>>>
>>> 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.
>>>
>>> GCC provides a way to deal with it by using
>>> __builtin_alloca_with_align(). Use it to avoid the bouncing cache lines.
>>
>> Eww.  How about __aligned?
>
> Err.. Stupid me. For some reason I remembered I tried it and it didnât have
> the desired effect, which caused me to assume it does not work for variables
> on the stack. Anyhow, it does the work. Iâll submit v2.
>

You're probably remembering that __aligned(16) malfunctions on older
GCC versions.  But __aligned(64), which is what you want, has always
been okay AFAIK.