Messages in this thread | | | Date | Tue, 14 Nov 2017 11:10:23 -0800 (PST) | From | Hugh Dickins <> | Subject | Re: [PATCH 18/30] x86, kaiser: map virtually-addressed performance monitoring buffers |
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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?
Hugh
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