perf: builtin-record: Document and check that mmap_pages must be a power of two.

Now that we automatically point users at it, let's provide them some
guidance so that they hopefully don't just get mysterious EINVAL's
from the kernel.

Cc: Ingo Molnar <mingo@elte.hu>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1324301972-22740-4-git-send-email-nelhage@nelhage.com
Signed-off-by: Nelson Elhage <nelhage@nelhage.com>
[ committer note: Made it work after 50a682c ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
This commit is contained in:
Nelson Elhage 2011-12-19 08:39:32 -05:00 committed by Arnaldo Carvalho de Melo
parent 18e6093904
commit 41d0d93349
4 changed files with 17 additions and 1 deletions

View File

@ -89,7 +89,7 @@ OPTIONS
-m::
--mmap-pages=::
Number of mmap data pages.
Number of mmap data pages. Must be a power of two.
-g::
--call-graph::

View File

@ -279,6 +279,9 @@ try_again:
"/proc/sys/kernel/perf_event_mlock_kb,\n"
"or try again with a smaller value of -m/--mmap_pages.\n"
"(current value: %d)\n", opts->mmap_pages);
else if (!is_power_of_2(opts->mmap_pages))
die("--mmap_pages/-m value must be a power of two.");
die("failed to mmap with %d (%s)\n", errno, strerror(errno));
}

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@ -563,6 +563,8 @@ int perf_evlist__mmap(struct perf_evlist *evlist, unsigned int pages,
/* 512 kiB: default amount of unprivileged mlocked memory */
if (pages == UINT_MAX)
pages = (512 * 1024) / page_size;
else if (!is_power_of_2(pages))
return -EINVAL;
mask = pages * page_size - 1;

View File

@ -245,4 +245,15 @@ int readn(int fd, void *buf, size_t size);
#define _STR(x) #x
#define STR(x) _STR(x)
/*
* Determine whether some value is a power of two, where zero is
* *not* considered a power of two.
*/
static inline __attribute__((const))
bool is_power_of_2(unsigned long n)
{
return (n != 0 && ((n & (n - 1)) == 0));
}
#endif