| Message ID | 1393271463-7722-1-git-send-email-kamal@canonical.com |
|---|---|
| State | New |
| Headers | show |
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index ce8514fe..8588689 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -2239,6 +2239,13 @@ __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer, write &= RB_WRITE_MASK; tail = write - length; + /* + * If this is the first commit on the page, then it has the same + * timestamp as the page itself. + */ + if (!tail) + delta = 0; + /* See if we shot pass the end of this buffer page */ if (unlikely(write > BUF_PAGE_SIZE)) return rb_move_tail(cpu_buffer, length, tail,
This is a note to let you know that I have just added a patch titled ring-buffer: Fix first commit on sub-buffer having non-zero delta to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree which can be found at: http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue This patch is scheduled to be released in version 3.8.13.19. If you, or anyone else, feels it should not be added to this tree, please reply to this email. For more information about the 3.8.y.z tree, see https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable Thanks. -Kamal ------ From ded17cf8e00759db0859bee996cd21482fb0fbd1 Mon Sep 17 00:00:00 2001 From: "Steven Rostedt (Red Hat)" <rostedt@goodmis.org> Date: Tue, 11 Feb 2014 13:38:54 -0500 Subject: ring-buffer: Fix first commit on sub-buffer having non-zero delta commit d651aa1d68a2f0a7ee65697b04c6a92f8c0a12f2 upstream. Each sub-buffer (buffer page) has a full 64 bit timestamp. The events on that page use a 27 bit delta against that timestamp in order to save on bits written to the ring buffer. If the time between events is larger than what the 27 bits can hold, a "time extend" event is added to hold the entire 64 bit timestamp again and the events after that hold a delta from that timestamp. As a "time extend" is always paired with an event, it is logical to just allocate the event with the time extend, to make things a bit more efficient. Unfortunately, when the pairing code was written, it removed the "delta = 0" from the first commit on a page, causing the events on the page to be slightly skewed. Fixes: 69d1b839f7ee "ring-buffer: Bind time extend and data events together" Signed-off-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Kamal Mostafa <kamal@canonical.com> --- kernel/trace/ring_buffer.c | 7 +++++++ 1 file changed, 7 insertions(+) -- 1.8.3.2