Messages in this thread Patch in this message | | | Date | Wed, 09 Jun 2021 18:43:10 -0400 | From | Steven Rostedt <> | Subject | [PATCH 1/2 v2] tracing: Simplify the max length test when using the filtering temp buffer |
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From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>
When filtering trace events, a temp buffer is used because the extra copy from the temp buffer into the ring buffer is still faster than the direct write into the ring buffer followed by a discard if the filter does not match.
But the data that can be stored in the temp buffer is a PAGE_SIZE minus the ring buffer event header. The calculation of that header size is complex, but using the helper macro "struct_size()" can simplify it.
Link: https://lore.kernel.org/stable/CAHk-=whKbJkuVmzb0hD3N6q7veprUrSpiBHRxVY=AffWZPtxmg@mail.gmail.com/
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org> --- Changes since v1: Switch "unlikely" to "likely" Test max_len <= instead of just <
kernel/trace/trace.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index f6c4d9cf0377..3366922076e6 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -2737,8 +2737,10 @@ trace_event_buffer_lock_reserve(struct trace_buffer **current_rb, (trace_file->flags & (EVENT_FILE_FL_SOFT_DISABLED | EVENT_FILE_FL_FILTERED)) && (entry = this_cpu_read(trace_buffered_event))) { /* Try to use the per cpu buffer first */ + int max_len = PAGE_SIZE - struct_size(entry, array, 1); + val = this_cpu_inc_return(trace_buffered_event_cnt); - if ((len < (PAGE_SIZE - sizeof(*entry) - sizeof(entry->array[0]))) && val == 1) { + if (val == 1 && likely(len <= max_len)) { trace_event_setup(entry, type, trace_ctx); entry->array[0] = len; return entry; -- 2.30.2
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