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Commit 41d0d933 authored by Nelson Elhage's avatar Nelson Elhage Committed by Arnaldo Carvalho de Melo
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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: default avatarNelson Elhage <nelhage@nelhage.com>
[ committer note: Made it work after 50a682ce ]
Signed-off-by: default avatarArnaldo Carvalho de Melo <acme@redhat.com>
parent 18e60939

tools/perf/Documentation/perf-record.txt

+1 −1
Original line number Diff line number Diff line
@@ -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::

tools/perf/builtin-record.c

+3 −0
Original line number Diff line number Diff line
@@ -279,6 +279,9 @@ static void perf_record__open(struct perf_record *rec) 
			    "/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));

	}

tools/perf/util/evlist.c

+2 −0
Original line number Diff line number Diff line
@@ -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;

tools/perf/util/util.h

+11 −0
Original line number Diff line number Diff line
@@ -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