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SubjectRe: [RFC PATCH v2 3/3] x86/mm/tlb: Avoid deferring PTI flushes on shootdown
On Fri, Aug 23, 2019 at 11:13 PM Nadav Amit <namit@vmware.com> wrote:
>
> When a shootdown is initiated, the initiating CPU has cycles to burn as
> it waits for the responding CPUs to receive the IPI and acknowledge it.
> In these cycles it is better to flush the user page-tables using
> INVPCID, instead of deferring the TLB flush.
>
> The best way to figure out whether there are cycles to burn is arguably
> to expose from the SMP layer when an acknowledgment is received.
> However, this would break some abstractions.
>
> Instead, use a simpler solution: the initiating CPU of a TLB shootdown
> would not defer PTI flushes. It is not always a win, relatively to
> deferring user page-table flushes, but it prevents performance
> regression.
>
> Signed-off-by: Nadav Amit <namit@vmware.com>
> ---
> arch/x86/include/asm/tlbflush.h | 1 +
> arch/x86/mm/tlb.c | 10 +++++++++-
> 2 files changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h
> index da56aa3ccd07..066b3804f876 100644
> --- a/arch/x86/include/asm/tlbflush.h
> +++ b/arch/x86/include/asm/tlbflush.h
> @@ -573,6 +573,7 @@ struct flush_tlb_info {
> unsigned int initiating_cpu;
> u8 stride_shift;
> u8 freed_tables;
> + u8 shootdown;

I find the name "shootdown" to be confusing. How about "more_than_one_cpu"?

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