Messages in this thread | | | From | Andy Lutomirski <> | Date | Tue, 14 Nov 2017 11:24:16 -0800 | Subject | Re: [PATCH 18/30] x86, kaiser: map virtually-addressed performance monitoring buffers |
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On Tue, Nov 14, 2017 at 11:10 AM, Hugh Dickins <hughd@google.com> wrote: > On Tue, 14 Nov 2017, Dave Hansen wrote: >> On 11/14/2017 10:20 AM, Peter Zijlstra wrote: >> > On Fri, Nov 10, 2017 at 11:31:39AM -0800, Dave Hansen wrote: >> >> static int alloc_ds_buffer(int cpu) >> >> { >> >> + struct debug_store *ds = per_cpu_ptr(&cpu_debug_store, cpu); >> >> >> >> + memset(ds, 0, sizeof(*ds)); >> > Still wondering about that memset... > > Sorry, my attention is far away at the moment. > >> >> My guess is that it was done to mirror the zeroing done by the original >> kzalloc(). > > You guess right. > >> But, I think you're right that it's zero'd already by virtue >> of being static: >> >> static >> DEFINE_PER_CPU_SHARED_ALIGNED_USER_MAPPED(struct debug_store, >> cpu_debug_store); >> >> I'll queue a cleanup, or update it if I re-post the set. > > I was about to agree, but now I'm not so sure. I don't know much > about these PMC things, but at a glance it looks like what is reserved > by x86_reserve_hardware() may later be released by x86_release_hardware(), > and then later reserved again by x86_reserve_hardware(). And although > the static per-cpu area would be zeroed the first time, the second time > it will contain data left over from before, so really needs the memset? >
For an upstream solution, I would really really like to see DEFINE_PER_CPU_SHARED_ALIGNED_USER_MAPPED and friends completely gone and to use cpu_entry_area instead. I don't know whether this has any material impact on this particular discussion, though.
--Andy
> Hugh
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