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SubjectRe: [RFC PATCH v2 3/3] x86/mm/tlb: Avoid deferring PTI flushes on shootdown
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> On Aug 27, 2019, at 4:07 PM, Andy Lutomirski <luto@kernel.org> wrote:
>
> 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”?

I think the current semantic is more of “includes remote cpus”. How about
calling it “local_only”, and negating its value?
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