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

Russ Anderson
2019-07-09T20:09:38Z

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 SGI UV support is outdated and not maintained, and it is not clear how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 - * and that IPI's action is out of date -- it does a manual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.
> > - */
> > - flush_tlb_func_local(info);
> > -
> > - cpumask = uv_flush_tlb_others(cpumask, info);
> > - if (cpumask)
> > - smp_call_function_many(cpumask, flush_tlb_func_remote,
> > - (void *)info, 1);
> > - return;
> > - }
> > -
> > /*
> > * If no page tables were freed, we can skip sending IPIs to
> > * CPUs in lazy TLB mode. They will flush the CPU themselves
> > --
> > 2.17.1
> >
> >

--
Russ Anderson, SuperDome Flex Linux Kernel Group Manager
HPE - Hewlett Packard Enterprise (formerly SGI) rja@hpe.com