powerpc: Add virtual processor dispatch trace log

pseries SPLPAR machines are able to retrieve a log of dispatch and
preempt events from the hypervisor. With this information, we can
see when and why each dispatch & preempt is occuring.

This change adds a set of debugfs files allowing userspace to read this
dispatch log.

Based on initial patches from Nishanth Aravamudan <nacc@us.ibm.com>.

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 10 insertions, 0 deletions

diff --git a/arch/powerpc/platforms/pseries/Kconfig b/arch/powerpc/platforms/pseries/Kconfig
index c0e6ec240f46..f0e6f28427bd 100644
--- a/arch/powerpc/platforms/pseries/Kconfig
+++ b/arch/powerpc/platforms/pseries/Kconfig
@@ -68,3 +68,13 @@ config CMM
           makes sense for a system running in an LPAR where the unused pages
           will be reused for other LPARs. The interface allows firmware to
           balance memory across many LPARs.
+
+config DTL
+        bool "Dispatch Trace Log"
+        depends on PPC_SPLPAR && DEBUG_FS
+        help
+          SPLPAR machines can log hypervisor preempt & dispatch events to a
+          kernel buffer. Saying Y here will enable logging these events,
+          which are accessible through a debugfs file.
+
+          Say N if you are unsure.