diff options
Diffstat (limited to 'Documentation/ftrace.txt')
-rw-r--r-- | Documentation/ftrace.txt | 22 |
1 files changed, 5 insertions, 17 deletions
diff --git a/Documentation/ftrace.txt b/Documentation/ftrace.txt index a1b58777839b..6d3fe4cdf921 100644 --- a/Documentation/ftrace.txt +++ b/Documentation/ftrace.txt | |||
@@ -94,10 +94,10 @@ of ftrace. Here is a list of some of the key files: | |||
94 | only be recorded if the latency is greater than | 94 | only be recorded if the latency is greater than |
95 | the value in this file. (in microseconds) | 95 | the value in this file. (in microseconds) |
96 | 96 | ||
97 | buffer_size_kb: This sets or displays the number of bytes each CPU | 97 | buffer_size_kb: This sets or displays the number of kilobytes each CPU |
98 | buffer can hold. The tracer buffers are the same size | 98 | buffer can hold. The tracer buffers are the same size |
99 | for each CPU. The displayed number is the size of the | 99 | for each CPU. The displayed number is the size of the |
100 | CPU buffer and not total size of all buffers. The | 100 | CPU buffer and not total size of all buffers. The |
101 | trace buffers are allocated in pages (blocks of memory | 101 | trace buffers are allocated in pages (blocks of memory |
102 | that the kernel uses for allocation, usually 4 KB in size). | 102 | that the kernel uses for allocation, usually 4 KB in size). |
103 | If the last page allocated has room for more bytes | 103 | If the last page allocated has room for more bytes |
@@ -1306,28 +1306,16 @@ the full size, multiply the number of possible CPUS with the | |||
1306 | number of entries. | 1306 | number of entries. |
1307 | 1307 | ||
1308 | # cat /debug/tracing/buffer_size_kb | 1308 | # cat /debug/tracing/buffer_size_kb |
1309 | 65620 | 1309 | 1408 (units kilobytes) |
1310 | 1310 | ||
1311 | Note, to modify this, you must have tracing completely disabled. To do that, | 1311 | Note, to modify this, you must have tracing completely disabled. To do that, |
1312 | echo "nop" into the current_tracer. If the current_tracer is not set | 1312 | echo "nop" into the current_tracer. If the current_tracer is not set |
1313 | to "nop", an EINVAL error will be returned. | 1313 | to "nop", an EINVAL error will be returned. |
1314 | 1314 | ||
1315 | # echo nop > /debug/tracing/current_tracer | 1315 | # echo nop > /debug/tracing/current_tracer |
1316 | # echo 100000 > /debug/tracing/buffer_size_kb | 1316 | # echo 10000 > /debug/tracing/buffer_size_kb |
1317 | # cat /debug/tracing/buffer_size_kb | 1317 | # cat /debug/tracing/buffer_size_kb |
1318 | 100045 | 1318 | 10000 (units kilobytes) |
1319 | |||
1320 | |||
1321 | Notice that we echoed in 100,000 but the size is 100,045. The entries | ||
1322 | are held in individual pages. It allocates the number of pages it takes | ||
1323 | to fulfill the request. If more entries may fit on the last page | ||
1324 | then they will be added. | ||
1325 | |||
1326 | # echo 1 > /debug/tracing/buffer_size_kb | ||
1327 | # cat /debug/tracing/buffer_size_kb | ||
1328 | 85 | ||
1329 | |||
1330 | This shows us that 85 entries can fit in a single page. | ||
1331 | 1319 | ||
1332 | The number of pages which will be allocated is limited to a percentage | 1320 | The number of pages which will be allocated is limited to a percentage |
1333 | of available memory. Allocating too much will produce an error. | 1321 | of available memory. Allocating too much will produce an error. |