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

[Mike Travis]

On 7/9/2019 2:09 PM, Nadav Amit wrote:
> > On Jul 9, 2019, at 1:29 PM, Mike Travis <mike.travis@xxxxxxx> 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 SGI UV support is outdated and not maintained, and it is not clear how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@xxxxxxxxxxxxx>
> > > > > Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
> > > > > Suggested-by: Andy Lutomirski <luto@xxxxxxxxxx>
> > > > > Signed-off-by: Nadav Amit <namit@xxxxxxxxxx>
> > > > > ---
> > > > >   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 -		 * and that IPI's action is out of date -- it does a manual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@xxxxxxx>

> Thanks,
> Nadav