Re: [PATCH 3/4] gcov: add gcov profiling infrastructure

Michael Ellerman
2009-06-03T16:01:16Z

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On Wed, 2009-06-03 at 17:26 +0200, Peter Oberparleiter wrote:
> Peter Oberparleiter wrote:
> > Andrew Morton wrote:
> >> On Tue, 02 Jun 2009 13:44:02 +0200
> >> Peter Oberparleiter <oberpar@linux.vnet.ibm.com> wrote:
> >>> + /* Duplicate gcov_info. */
> >>> + active = num_counter_active(info);
> >>> + dup = kzalloc(sizeof(struct gcov_info) +
> >>> + sizeof(struct gcov_ctr_info) * active, GFP_KERNEL);
> >>
> >> How large can this allocation be?
> >
> > Hm, good question. Having a look at my test system, I see coverage data
> > files of up to 60kb size. With counters making up the largest part of
> > those, I'd guess the allocation size can be around ~55kb. I assume that
> > makes it a candidate for vmalloc?
>
> A further run with debug output showed that the maximum size is
> actually around 4k, so in my opinion, there is no need to switch
> to vmalloc.

The real question is how big can active be, and it looks like <= 5 is
the answer:

+/* Determine number of active counters. Based on gcc magic. */
+static unsigned int num_counter_active(struct gcov_info *info)
+{
+ unsigned int i;
+ unsigned int result = 0;
+
+ for (i = 0; i < GCOV_COUNTERS; i++) {
+ if (counter_active(info, i))
+ result++;
+ }
+ return result;
+}

+#define GCOV_COUNTERS 5

So that seems reasonable.

I assumed these were the per BB counters, but it seems they're counter
_types_. Where are the BB counters, in the values array? If so perhaps
that is the candidate for vmalloc.

cheers

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