Re: [PATCH v2 8/9] x86/mm/tlb: Remove UV special case

Mike Travis
2019-07-09T21:17:39Z

On 7/9/2019 2:09 PM, Nadav Amit wrote:
>> On Jul 9, 2019, at 1:29 PM, Mike Travis <mike.travis@hpe.com> wrote:
>>
>>
>>
>> On 7/9/2019 1:09 PM, Russ Anderson wrote:
>>> On Tue, Jul 09, 2019 at 09:50:27PM +0200, Thomas Gleixner wrote:
>>>> On Tue, 2 Jul 2019, Nadav Amit wrote:
>>>>
>>>>> SGI UV support is outdated and not maintained, and it is not clear how
>>>>> it performs relatively to non-UV. Remove the code to simplify the code.
>>>>
>>>> You should at least Cc the SGI/HP folks on that. They are still
>>>> around. Done so.
>>> Thanks Thomas. The SGI UV is now HPE Superdome Flex and is
>>> very much still supported.
>>> Thanks.
>>>>> Cc: Peter Zijlstra <peterz@infradead.org>
>>>>> Cc: Dave Hansen <dave.hansen@intel.com>
>>>>> Suggested-by: Andy Lutomirski <luto@kernel.org>
>>>>> Signed-off-by: Nadav Amit <namit@vmware.com>
>>>>> ---
>>>>> arch/x86/mm/tlb.c | 25 -------------------------
>>>>> 1 file changed, 25 deletions(-)
>>>>>
>>>>> diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
>>>>> index b47a71820f35..64afe1215495 100644
>>>>> --- a/arch/x86/mm/tlb.c
>>>>> +++ b/arch/x86/mm/tlb.c
>>>>> @@ -689,31 +689,6 @@ void native_flush_tlb_multi(const struct cpumask *cpumask,
>>>>> trace_tlb_flush(TLB_REMOTE_SEND_IPI,
>>>>> (info->end - info->start) >> PAGE_SHIFT);
>>>>> - if (is_uv_system()) {
>>>>> - /*
>>>>> - * This whole special case is confused. UV has a "Broadcast
>>>>> - * Assist Unit", which seems to be a fancy way to send IPIs.
>>>>> - * Back when x86 used an explicit TLB flush IPI, UV was
>>>>> - * optimized to use its own mechanism. These days, x86 uses
>>>>> - * smp_call_function_many(), but UV still uses a manual IPI,
>>>>> - * and that IPI's action is out of date -- it does a manual
>>>>> - * flush instead of calling flush_tlb_func_remote(). This
>>>>> - * means that the percpu tlb_gen variables won't be updated
>>>>> - * and we'll do pointless flushes on future context switches.
>>>>> - *
>>>>> - * Rather than hooking native_flush_tlb_multi() here, I think
>>>>> - * that UV should be updated so that smp_call_function_many(),
>>>>> - * etc, are optimal on UV.
>>>>> - */
>>
>> I thought this change was already proposed a bit ago and we acked it
>> awhile back. Also the replacement functionality is being worked on but it
>> is more complex. The smp call many has to support all the reasons why it’s
>> called and not just the tlb shoot downs as is the current BAU case.
>
> Sorry for not cc’ing you before. In the meanwhile, can you give an explicit
> acked-by? (I couldn’t find the previous patch you regarded.)

Sure:

Acked-by: Mike Travis <mike.travis@hpe.com>

>
> Thanks,
> Nadav
>