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authorKOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>2010-07-01 14:34:35 +0900
committerSteven Rostedt <rostedt@goodmis.org>2010-07-21 10:20:17 -0400
commitef710e100c1068d3dd5774d2b34c5485219e06ce (patch)
treeed295053a31de472d4ed4338679c00ac8e8437c7 /kernel/trace/trace_sched_wakeup.c
parentbc289ae98b75d93228d24f521ef02a076e506e94 (diff)
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tracing: Shrink max latency ringbuffer if unnecessary
Documentation/trace/ftrace.txt says buffer_size_kb: This sets or displays the number of kilobytes each CPU buffer can hold. The tracer buffers are the same size for each CPU. The displayed number is the size of the CPU buffer and not total size of all buffers. The trace buffers are allocated in pages (blocks of memory that the kernel uses for allocation, usually 4 KB in size). If the last page allocated has room for more bytes than requested, the rest of the page will be used, making the actual allocation bigger than requested. ( Note, the size may not be a multiple of the page size due to buffer management overhead. ) This can only be updated when the current_tracer is set to "nop". But it's incorrect. currently total memory consumption is 'buffer_size_kb x CPUs x 2'. Why two times difference is there? because ftrace implicitly allocate the buffer for max latency too. That makes sad result when admin want to use large buffer. (If admin want full logging and makes detail analysis). example, If admin have 24 CPUs machine and write 200MB to buffer_size_kb, the system consume ~10GB memory (200MB x 24 x 2). umm.. 5GB memory waste is usually unacceptable. Fortunatelly, almost all users don't use max latency feature. The max latency buffer can be disabled easily. This patch shrink buffer size of the max latency buffer if unnecessary. Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> LKML-Reference: <20100701104554.DA2D.A69D9226@jp.fujitsu.com> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Diffstat (limited to 'kernel/trace/trace_sched_wakeup.c')
-rw-r--r--kernel/trace/trace_sched_wakeup.c2
1 files changed, 2 insertions, 0 deletions
diff --git a/kernel/trace/trace_sched_wakeup.c b/kernel/trace/trace_sched_wakeup.c
index c9fd5bd0203..4086eae6e81 100644
--- a/kernel/trace/trace_sched_wakeup.c
+++ b/kernel/trace/trace_sched_wakeup.c
@@ -382,6 +382,7 @@ static struct tracer wakeup_tracer __read_mostly =
#ifdef CONFIG_FTRACE_SELFTEST
.selftest = trace_selftest_startup_wakeup,
#endif
+ .use_max_tr = 1,
};
static struct tracer wakeup_rt_tracer __read_mostly =
@@ -396,6 +397,7 @@ static struct tracer wakeup_rt_tracer __read_mostly =
#ifdef CONFIG_FTRACE_SELFTEST
.selftest = trace_selftest_startup_wakeup,
#endif
+ .use_max_tr = 1,
};
__init static int init_wakeup_tracer(void)