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ring-buffer: only allocate buffers for online cpus

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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: Steven Rostedt <srostedt@redhat.com>
This commit is contained in:
Steven Rostedt
2009-03-11 22:00:13 -04:00
parent 9aba60fe6e
commit 554f786e28
2 changed files with 217 additions and 57 deletions
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6
kernel/trace/trace.c
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@ -1805,17 +1805,11 @@ __tracing_open(struct inode *inode, struct file *file)
iter->buffer_iter[cpu] =
ring_buffer_read_start(iter->tr->buffer, cpu);
if (!iter->buffer_iter[cpu])
goto fail_buffer;
}
} else {
cpu = iter->cpu_file;
iter->buffer_iter[cpu] =
ring_buffer_read_start(iter->tr->buffer, cpu);
if (!iter->buffer_iter[cpu])
goto fail;
}
/* TODO stop tracer */