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  1. 16 Jun, 2009 3 commits
    • Steven Rostedt's avatar
      ring-buffer: use commit counters for commit pointer accounting · fa743953
      Steven Rostedt authored 
      The ring buffer is made up of three sets of pointers.

The head page pointer, which points to the next page for the reader to
get.

The commit pointer and commit index, which points to the page and index
of the last committed write respectively.

The tail pointer and tail index, which points to the page and the index
of the last reserved data respectively (non committed).

The commit pointer is only moved forward by the outer most writer.
If a nested writer comes in, it will not move the pointer forward.

The current implementation has a flaw. It assumes that the outer most
writer successfully reserved data. There's a small race window where
the outer most writer could find the tail pointer, but a nested
writer could come in (via interrupt) and move the tail forward, and
even the commit forward.

The outer writer would not realized the commit moved forward and the
accounting will break.

This patch changes the design to use counters in the per cpu buffers
to keep track of commits. The counters are incremented at the start
of the commit, and decremented at the end. If the end commit counter
is 1, then it moves the commit pointers. A loop is made to check for
races between checking and moving the commit pointers. Only the outer
commit should move the pointers anyway.

The test of knowing if a reserve is equal to the last commit update
is still needed to know for time keeping. The time code is much less
racey than the commit updates.

This change not only solves the mentioned race, but also makes the
code simpler.

[ Impact: fix commit race and simplify code ]
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
      fa743953
    • Steven Rostedt's avatar
      ring-buffer: remove unused variable · 263294f3
      Steven Rostedt authored 
      Fix the compiler error:

kernel/trace/ring_buffer.c: In function 'rb_move_tail':
kernel/trace/ring_buffer.c:1236: warning: unused variable 'event'
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
      263294f3
    • Steven Rostedt's avatar
      ring-buffer: have benchmark test handle discarded events · 9086c7b9
      Steven Rostedt authored 
      With the addition of commit:

  c7b09308
  ring-buffer: prevent adding write in discarded area

The ring buffer may now add discarded events when a write passes
the end of a buffer page. Before, a discarded event was only added
when the tracer deliberately created one. The ring buffer benchmark
test does not handle discarded events when it reads the buffer and
fails when it encounters one.

Also fix the increment for large data entries (luckily, the test did
not add any yet).

[ Impact: fix false failure of ring buffer self test ]
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
      9086c7b9
  3. 15 Jun, 2009 7 commits
  5. 14 Jun, 2009 30 commits