Re: [PATCH v4 RESEND 3/5] perf/x86/lbr: Move cpuc->lbr_xsave allocation out of sleeping region

[Like Xu]

On 2021/3/24 12:04, Namhyung Kim wrote:
> On Wed, Mar 24, 2021 at 12:47 PM Like Xu <like.xu@xxxxxxxxxxxxxxx> wrote:
> > Hi Namhyung,
> >
> > On 2021/3/24 9:32, Namhyung Kim wrote:
> > > Hello,
> > >
> > > On Mon, Mar 22, 2021 at 3:14 PM Like Xu <like.xu@xxxxxxxxxxxxxxx> wrote:
> > > > +void reserve_lbr_buffers(struct perf_event *event)
> > > > +{
> > > > +       struct kmem_cache *kmem_cache = x86_get_pmu()->task_ctx_cache;
> > > > +       struct cpu_hw_events *cpuc;
> > > > +       int cpu;
> > > > +
> > > > +       if (!static_cpu_has(X86_FEATURE_ARCH_LBR))
> > > > +               return;
> > > > +
> > > > +       for_each_possible_cpu(cpu) {
> > > > +               cpuc = per_cpu_ptr(&cpu_hw_events, cpu);
> > > > +               if (kmem_cache && !cpuc->lbr_xsave && !event->attr.precise_ip)
> > > > +                       cpuc->lbr_xsave = kmem_cache_alloc(kmem_cache, GFP_KERNEL);
> > > > +       }
> > > > +}
> > >
> > > I think we should use kmem_cache_alloc_node().
> >
> > "kmem_cache_alloc_node - Allocate an object on the specified node"
> >
> > The reserve_lbr_buffers() is called in __x86_pmu_event_init().
> > When the LBR perf_event is scheduled to another node, it seems
> > that we will not call init() and allocate again.
> >
> > Do you mean use kmem_cache_alloc_node() for each numa_nodes_parsed ?
>
> I assume cpuc->lbr_xsave will be accessed for that cpu only.
> Then it needs to allocate it in the node that cpu belongs to.
> Something like below..
>
>      cpuc->lbr_xsave = kmem_cache_alloc_node(kmem_cache, GFP_KERNEL,
>                                                 cpu_to_node(cpu));

Thanks, it helps and I will apply it in the next version.

> Thanks,
> Namhyung