Re: [PATCH] x86: Align TLB invalidation info

[Nadav Amit]

Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> wrote:

> On 01/31/2018 12:48 PM, Nadav Amit 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.
> 
> Also, just curious, but did you find this situation by inspection or did
> it show up in a profile somewhere?

Actually, not. I considered adding data to info for a different reason
(which eventually I deserted); I was assuming you will all kill me for
increasing the size, so this was a preemption step.