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

Nadav Amit
2019-07-09T21:09:20Z

> 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 SGI UV support is outdated and not maintained, and it is not clear how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 - * and that IPI's action is out of date -- it does a manual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.)

Thanks,
Nadav