Messages in this thread Patch in this message | | | From | Douglas Anderson <> | Subject | [PATCH v3] tracing: kdb: Allow ftdump to skip all but the last few lines | Date | Fri, 15 Mar 2019 10:45:28 -0700 |
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The 'ftdump' command in kdb is currently a bit of a last resort, at least if you have lots of traces turned on. It's going to print a whole boatload of lines out your serial port which is probably running at 115200. This could easily take many, many minutes.
Usually you're most interested in what's at the _end_ of the ftrace buffer, AKA what happened most recently. That means you've got to wait the full time for the dump. The 'ftdump' command does attempt to help you a little bit by allowing you to skip a fixed number of lines. Unfortunately it provides no way for you to know how many lines you should skip.
Let's do similar to python and allow you to use a negative number to indicate that you want to skip all lines except the last few. This allows you to quickly see what you want.
Signed-off-by: Douglas Anderson <dianders@chromium.org> ---
Changes in v3: - Optimize counting as per Steven Rostedt. - Down to 1 patch since patch #1 from v2 landed.
kernel/trace/trace_kdb.c | 38 +++++++++++++++++++++++++++++--------- 1 file changed, 29 insertions(+), 9 deletions(-)
diff --git a/kernel/trace/trace_kdb.c b/kernel/trace/trace_kdb.c index 810d78a8d14c..cc6ca6c0d6de 100644 --- a/kernel/trace/trace_kdb.c +++ b/kernel/trace/trace_kdb.c @@ -17,7 +17,7 @@ #include "trace.h" #include "trace_output.h" -static void ftrace_dump_buf(int skip_lines, long cpu_file) +static int ftrace_dump_buf(int skip_lines, long cpu_file, bool quiet) { /* use static because iter can be a bit big for the stack */ static struct trace_iterator iter; @@ -39,8 +39,6 @@ static void ftrace_dump_buf(int skip_lines, long cpu_file) /* don't look at user memory in panic mode */ tr->trace_flags &= ~TRACE_ITER_SYM_USEROBJ; - kdb_printf("Dumping ftrace buffer:\n"); - /* reset all but tr, trace, and overruns */ memset(&iter.seq, 0, sizeof(struct trace_iterator) - @@ -55,6 +53,9 @@ static void ftrace_dump_buf(int skip_lines, long cpu_file) cpu, GFP_ATOMIC); ring_buffer_read_start(iter.buffer_iter[cpu]); tracing_iter_reset(&iter, cpu); + + cnt += + ring_buffer_entries_cpu(iter.trace_buffer->buffer, cpu); } } else { iter.cpu_file = cpu_file; @@ -63,13 +64,21 @@ static void ftrace_dump_buf(int skip_lines, long cpu_file) cpu_file, GFP_ATOMIC); ring_buffer_read_start(iter.buffer_iter[cpu_file]); tracing_iter_reset(&iter, cpu_file); + + cnt += ring_buffer_entries_cpu(iter.trace_buffer->buffer, + cpu_file); } - while (trace_find_next_entry_inc(&iter)) { - if (!cnt) - kdb_printf("---------------------------------\n"); - cnt++; + if (quiet) + goto out; + + kdb_printf("Dumping ftrace buffer (skipping %d lines):\n", + skip_lines); + + if (cnt) + kdb_printf("---------------------------------\n"); + while (trace_find_next_entry_inc(&iter)) { if (!skip_lines) { print_trace_line(&iter); trace_printk_seq(&iter.seq); @@ -99,6 +108,8 @@ static void ftrace_dump_buf(int skip_lines, long cpu_file) iter.buffer_iter[cpu] = NULL; } } + + return cnt; } /* @@ -109,6 +120,7 @@ static int kdb_ftdump(int argc, const char **argv) int skip_lines = 0; long cpu_file; char *cp; + int cnt; if (argc > 2) return KDB_ARGCOUNT; @@ -129,7 +141,14 @@ static int kdb_ftdump(int argc, const char **argv) } kdb_trap_printk++; - ftrace_dump_buf(skip_lines, cpu_file); + + /* A negative skip_lines means skip all but the last lines */ + if (skip_lines < 0) { + cnt = ftrace_dump_buf(0, cpu_file, true); + skip_lines = max(cnt + skip_lines, 0); + } + + ftrace_dump_buf(skip_lines, cpu_file, false); kdb_trap_printk--; return 0; @@ -138,7 +157,8 @@ static int kdb_ftdump(int argc, const char **argv) static __init int kdb_ftrace_register(void) { kdb_register_flags("ftdump", kdb_ftdump, "[skip_#lines] [cpu]", - "Dump ftrace log", 0, KDB_ENABLE_ALWAYS_SAFE); + "Dump ftrace log; -skip dumps last #lines", 0, + KDB_ENABLE_ALWAYS_SAFE); return 0; } -- 2.21.0.360.g471c308f928-goog
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