Make TRACE() buffer size configurable

Let the user choose an appropriate buffer size (instead of scaling
with NR_CPUS).  The kfifo api requires the buffer to be a power of
two, so enforce this constraint in the configuration.

This fixes a previously-existing compile-time error for values of
NR_CPU that are not a power of two.

Based on a patch by Mac Mollison <mollison@cs.unc.edu>.

1 files changed, 20 insertions, 0 deletions

diff --git a/litmus/Kconfig b/litmus/Kconfig
index f1de6fabfc17..a3341021f05c 100644
--- a/litmus/Kconfig
+++ b/litmus/Kconfig
@@ -149,6 +149,26 @@ config SCHED_DEBUG_TRACE
           Say Yes for debugging.
           Say No for overhead tracing.
 
+config SCHED_DEBUG_TRACE_SHIFT
+       int "Buffer size for TRACE() buffer"
+       depends on SCHED_DEBUG_TRACE
+       range 14 22
+       default 18
+       help
+
+        Select the amount of memory needed per CPU for the TRACE() buffer, as a
+        power of two. The TRACE() buffer is global and statically allocated. If
+        the buffer is too small, there will be holes in the TRACE() log if the
+        buffer-flushing task is starved.
+
+        The default should be sufficient for most systems. Increase the buffer
+        size if the log contains holes. Reduce the buffer size when running on
+        a memory-constrained system.
+
+        Examples: 14 =>  16KB
+                  18 => 256KB
+                  20 =>   1MB
+
 endmenu
 
 endmenu