Messages in this thread Patch in this message | | | From | Nelson Elhage <> | Subject | [PATCH 3/3] perf: builtin-record: Document and check that mmap_pages must be a power of two. | Date | Mon, 19 Dec 2011 08:39:32 -0500 |
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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.
Signed-off-by: Nelson Elhage <nelhage@nelhage.com> --- tools/perf/Documentation/perf-record.txt | 2 +- tools/perf/builtin-record.c | 3 +++ tools/perf/util/util.h | 11 +++++++++++ 3 files changed, 15 insertions(+), 1 deletions(-)
diff --git a/tools/perf/Documentation/perf-record.txt b/tools/perf/Documentation/perf-record.txt index 5a520f8..2937f7e 100644 --- a/tools/perf/Documentation/perf-record.txt +++ b/tools/perf/Documentation/perf-record.txt @@ -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:: diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c index 45b23c1..275c78d 100644 --- a/tools/perf/builtin-record.c +++ b/tools/perf/builtin-record.c @@ -560,6 +560,9 @@ static int __cmd_record(int argc, const char **argv) if (mmap_pages == UINT_MAX) mmap_pages = (512 * 1024) / page_size; + if (!is_power_of_2(mmap_pages)) + die("--mmap_pages/-m value must be a power of two."); + if (forks) { child_pid = fork(); if (child_pid < 0) { diff --git a/tools/perf/util/util.h b/tools/perf/util/util.h index 0128906..37be34d 100644 --- a/tools/perf/util/util.h +++ b/tools/perf/util/util.h @@ -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 -- 1.7.4.41.g50b8f
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