oprofile, x86: Add comments to IBS LVT offset initialization

Adding a comment in the code as IBS LVT setup is not obvious at all ...

Signed-off-by: Robert Richter <robert.richter@amd.com>

1 files changed, 9 insertions, 4 deletions

diff --git a/arch/x86/oprofile/op_model_amd.c b/arch/x86/oprofile/op_model_amd.c
index 9fd8a567fe1e..9cbb710dc94b 100644
--- a/arch/x86/oprofile/op_model_amd.c
+++ b/arch/x86/oprofile/op_model_amd.c
@@ -609,16 +609,21 @@ static int setup_ibs_ctl(int ibs_eilvt_off)
         return 0;
 }
 
+/*
+ * This runs only on the current cpu. We try to find an LVT offset and
+ * setup the local APIC. For this we must disable preemption. On
+ * success we initialize all nodes with this offset. This updates then
+ * the offset in the IBS_CTL per-node msr. The per-core APIC setup of
+ * the IBS interrupt vector is called from op_amd_setup_ctrs()/op_-
+ * amd_cpu_shutdown() using the new offset.
+ */
 static int force_ibs_eilvt_setup(void)
 {
         int offset;
         int ret;
 
-        /*
-         * find the next free available EILVT entry, skip offset 0,
-         * pin search to this cpu
-         */
         preempt_disable();
+        /* find the next free available EILVT entry, skip offset 0 */
         for (offset = 1; offset < APIC_EILVT_NR_MAX; offset++) {
                 if (get_eilvt(offset))
                         break;