2 files changed, 24 insertions, 3 deletions

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 2b8ee90bb644..2623749ae7a3 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -5173,6 +5173,13 @@
                         with /sys/devices/system/xen_memory/xen_memory0/scrub_pages.
                         Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT.
 
+        xen_timer_slop= [X86-64,XEN]
+                        Set the timer slop (in nanoseconds) for the virtual Xen
+                        timers (default is 100000). This adjusts the minimum
+                        delta of virtualized Xen timers, where lower values
+                        improve timer resolution at the expense of processing
+                        more timer interrupts.
+
         xirc2ps_cs=     [NET,PCMCIA]
                         Format:
                         <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
index 6e29794573b7..befbdd8b17f0 100644
--- a/arch/x86/xen/time.c
+++ b/arch/x86/xen/time.c
@@ -28,7 +28,7 @@
 
 #include "xen-ops.h"
 
-/* Xen may fire a timer up to this many ns early */
+/* Minimum amount of time until next clock event fires */
 #define TIMER_SLOP      100000
 
 static u64 xen_sched_clock_offset __read_mostly;
@@ -212,7 +212,7 @@ static int xen_timerop_set_next_event(unsigned long delta,
         return 0;
 }
 
-static const struct clock_event_device xen_timerop_clockevent = {
+static struct clock_event_device xen_timerop_clockevent __ro_after_init = {
         .name                   = "xen",
         .features               = CLOCK_EVT_FEAT_ONESHOT,
 
@@ -273,7 +273,7 @@ static int xen_vcpuop_set_next_event(unsigned long delta,
         return ret;
 }
 
-static const struct clock_event_device xen_vcpuop_clockevent = {
+static struct clock_event_device xen_vcpuop_clockevent __ro_after_init = {
         .name = "xen",
         .features = CLOCK_EVT_FEAT_ONESHOT,
 
@@ -570,3 +570,17 @@ void __init xen_hvm_init_time_ops(void)
         x86_platform.set_wallclock = xen_set_wallclock;
 }
 #endif
+
+/* Kernel parameter to specify Xen timer slop */
+static int __init parse_xen_timer_slop(char *ptr)
+{
+        unsigned long slop = memparse(ptr, NULL);
+
+        xen_timerop_clockevent.min_delta_ns = slop;
+        xen_timerop_clockevent.min_delta_ticks = slop;
+        xen_vcpuop_clockevent.min_delta_ns = slop;
+        xen_vcpuop_clockevent.min_delta_ticks = slop;
+
+        return 0;
+}
+early_param("xen_timer_slop", parse_xen_timer_slop);