vdso: Add comment about reason for vdso struct ordering

struct vdso_data is optimized for fast access to the often required struct
members. The optimization is not documented in the struct description but
it should be kept in mind, when working with the vdso_data struct.

Add a comment to the struct description.

Signed-off-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Link: https://lore.kernel.org/r/20240701-vdso-cleanup-v1-2-36eb64e7ece2@linutronix.de

diff --git a/include/vdso/datapage.h b/include/vdso/datapage.h
index d04d394db064aec1283366e5abf57bc4c010d9ea..7647e0946f5008d61ec6075b122821db0da52aac 100644 (file)
--- a/include/vdso/datapage.h
+++ b/include/vdso/datapage.h
@@ -77,6 +77,10 @@ struct vdso_timestamp {
  * vdso_data will be accessed by 64 bit and compat code at the same time
  * so we should be careful before modifying this structure.
  *
+ * The ordering of the struct members is optimized to have fast access to the
+ * often required struct members which are related to CLOCK_REALTIME and
+ * CLOCK_MONOTONIC. This information is stored in the first cache lines.
+ *
  * @basetime is used to store the base time for the system wide time getter
  * VVAR page.
  *