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authorRyan Thibodeaux <ryan.thibodeaux@starlab.io>2019-03-22 14:29:57 -0400
committerBoris Ostrovsky <boris.ostrovsky@oracle.com>2019-04-23 11:06:26 -0400
commit2ec16bc0fc7ab544f2d405fd4fdd0d717c5ec0c5 (patch)
treefeb11296447e1e1c12a5cd1888d3a177d587c82c /arch/x86/xen
parent085b7755808aa11f78ab9377257e1dad2e6fa4bb (diff)
downloadlinux-2ec16bc0fc7ab544f2d405fd4fdd0d717c5ec0c5.tar.bz2
x86/xen: Add "xen_timer_slop" command line option
Add a new command-line option "xen_timer_slop=<INT>" that sets the minimum delta of virtual Xen timers. This commit does not change the default timer slop value for virtual Xen timers. Lowering the timer slop value should improve the accuracy of virtual timers (e.g., better process dispatch latency), but it will likely increase the number of virtual timer interrupts (relative to the original slop setting). The original timer slop value has not changed since the introduction of the Xen-aware Linux kernel code. This commit provides users an opportunity to tune timer performance given the refinements to hardware and the Xen event channel processing. It also mirrors a feature in the Xen hypervisor - the "timer_slop" Xen command line option. [boris: updated comment describing TIMER_SLOP] Signed-off-by: Ryan Thibodeaux <ryan.thibodeaux@starlab.io> Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Diffstat (limited to 'arch/x86/xen')
-rw-r--r--arch/x86/xen/time.c20
1 files changed, 17 insertions, 3 deletions
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);