Re: [PATCH] x86/platform/uv/BAU: disable BAU on single hub configurations
From: Andrew Banman
Date: Thu Jul 20 2017 - 14:56:06 EST
On Thu, Jul 20, 2017 at 01:47:50PM +0200, Ingo Molnar wrote:
>
> * Andrew Banman <abanman@xxxxxxx> wrote:
>
> > The BAU confers no benefit to a UV system running with only one hub/socket.
> > Permanently disable the BAU driver if there are less than two hubs online
> > to avoid BAU overhead. We have observed failed boots on single-socket UV4
> > systems caused by BAU that are avoided with this patch.
> >
> > Signed-off-by: Andrew Banman <abanman@xxxxxxx>
> > Acked-by: Russ Anderson <rja@xxxxxxx>
> > Acked-by: Mike Travis <mike.travis@xxxxxxx>
> > ---
> > arch/x86/platform/uv/tlb_uv.c | 6 ++++++
> > 1 file changed, 6 insertions(+)
> >
> > diff --git a/arch/x86/platform/uv/tlb_uv.c b/arch/x86/platform/uv/tlb_uv.c
> > index 2511a28..88216cc 100644
> > --- a/arch/x86/platform/uv/tlb_uv.c
> > +++ b/arch/x86/platform/uv/tlb_uv.c
> > @@ -2251,6 +2251,12 @@ static int __init uv_bau_init(void)
> > }
> >
> > nuvhubs = uv_num_possible_blades();
> > + if (nuvhubs < 2) {
> > + pr_crit("UV: BAU disabled - insufficient hub count\n");
> > + set_bau_off();
> > + nobau_perm = 1;
> > + return 0;
> > + }
>
> Yeah, could you structure the error paths in this function in a bit more organized
> fashion? It has two similar error handling blocks:
>
>
> pr_crit("UV: BAU disabled - insufficient hub count\n");
> set_bau_off();
> nobau_perm = 1;
> return 0;
>
> ...
>
> set_bau_off();
> nobau_perm = 1;
> return 0;
>
> which could be consolidated via the usual goto exception construct:
>
> if (nuvhubs < 2) {
> pr_crit("UV: BAU disabled - insufficient hub count\n");
> goto err_disable_bau;
> }
> ...
>
> if (init_per_cpu(nuvhubs, uv_base_pnode))
> pr_crit("UV: BAU disabled - per CPU init failed\n");
> goto err_disable_bau;
> }
>
> ...
> return 0;
>
> err_disable_bau:
>
> set_bau_off();
> nobau_perm = 1;
> return 0;
>
> Note that I added an error message to the second case as well.
>
> Plus, in the error case you might want to use a 'return -EINVAL;' instead of
> return 0, or so?
I agree with your suggestions, and I'm happy to make the changes.
>
> Plus plus, there's probably a (mild) memory leak in the error paths, can the
> cpumasks be free_cpumask_var() freed - or are they still required even if BAU is
> disabled?
In the case of nobau_perm=1 they can be freed. I will include that in the next
version.
>
> Thanks,
>
> Ingo
Thank you! I'll have the next version out shortly.
Andrew