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  1. 13 3月, 2009 25 次提交
  3. 12 3月, 2009 4 次提交
    • S
      ring-buffer: only allocate buffers for online cpus · 554f786e
      由 Steven Rostedt 提交于 
      Impact: save on memory

Currently, a ring buffer was allocated for each "possible_cpus". On
some systems, this is the same as NR_CPUS. Thus, if a system defined
NR_CPUS = 64 but it only had 1 CPU, we could have possibly 63 useless
ring buffers taking up space. With a default buffer of 3 megs, this
could be quite drastic.

This patch changes the ring buffer code to only allocate ring buffers
for online CPUs.  If a CPU goes off line, we do not free the buffer.
This is because the user may still have trace data in that buffer
that they would like to look at.

Perhaps in the future we could add code to delete a ring buffer if
the CPU is offline and the ring buffer becomes empty.
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>
      554f786e
    • S
      tracing: fix trace_wait to know to wait on all cpus or just one · 9aba60fe
      由 Steven Rostedt 提交于 
      Impact: fix to task live locking on reading trace_pipe on one CPU

The same code is used for both trace_pipe (all CPUS) and the per_cpu
trace_pipe file. When there is no data to read, it will check for
signals and wait on the trace wait queue.

The problem happens with the per_cpu wait. The trace_wait code checks
all CPUs. Thus, if there's data in another CPU buffer, then it will
exit the wait, without checking for signals or waiting on the wait queue.

It would then try to read the empty buffer, and since that will just
return nothing, then it will try to wait again. Unfortunately, that will
again fail due to there still being data in the other buffers. This
ends up with a live lock for the task.

This patch fixes the trace_wait to be aware that the iterator may only
be waiting on a single buffer.
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>
      9aba60fe
    • S
      tracing: expand the ring buffers when an event is activated · 1852fcce
      由 Steven Rostedt 提交于 
      To save memory, the tracer ring buffers are set to a minimum.
The activating of a trace expands the ring buffer size. This patch
adds this expanding, when an event is activated.
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>
      1852fcce
    • S
      tracing: keep ring buffer to minimum size till used · 73c5162a
      由 Steven Rostedt 提交于 
      Impact: less memory impact on systems not using tracer

When the kernel boots up that has tracing configured, it allocates
the default size of the ring buffer. This currently happens to be
1.4Megs per possible CPU. This is quite a bit of wasted memory if
the system is never using the tracer.

The current solution is to keep the ring buffers to a minimum size
until the user uses them. Once a tracer is piped into the current_tracer
the ring buffer will be expanded to the default size. If the user
changes the size of the ring buffer, it will take the size given
by the user immediately.

If the user adds a "ftrace=" to the kernel command line, then the ring
buffers will be set to the default size on initialization.
Signed-off-by: NSteven Rostedt <srostedt@redhat.com>
      73c5162a
  5. 11 3月, 2009 7 次提交
  7. 10 3月, 2009 4 次提交