On 09/25/2009 04:11 AM, Zhai, Edwin wrote:
Avi,
hrtimer is used for sleep in attached patch, which have similar perf
gain with previous one. Maybe we can check in this patch first, and
turn to direct yield in future, as you suggested.
+/*
+ * These 2 parameters are used to config the controls for Pause-Loop Exiting:
+ * ple_gap: upper bound on the amount of time between two successive
+ * executions of PAUSE in a loop. Also indicate if ple enabled.
+ * According to test, this time is usually small than 41 cycles.
+ * ple_window: upper bound on the amount of time a guest is allowed to execute
+ * in a PAUSE loop. Tests indicate that most spinlocks are held for
+ * less than 2^12 cycles
+ * Time is measured based on a counter that runs at the same rate as the TSC,
+ * refer SDM volume 3b section 21.6.13& 22.1.3.
+ */
+#define KVM_VMX_DEFAULT_PLE_GAP 41
+#define KVM_VMX_DEFAULT_PLE_WINDOW 4096
+static int __read_mostly ple_gap = KVM_VMX_DEFAULT_PLE_GAP;
+module_param(ple_gap, int, S_IRUGO);
+
+static int __read_mostly ple_window = KVM_VMX_DEFAULT_PLE_WINDOW;
+module_param(ple_window, int, S_IRUGO);
Shouldn't be __read_mostly since they're read very rarely (__read_mostly
should be for variables that are very often read, and rarely written).
I'm not even sure they should be parameters.
/*
+ * Indicate a busy-waiting vcpu in spinlock. We do not enable the PAUSE
+ * exiting, so only get here on cpu with PAUSE-Loop-Exiting.
+ */
+static int handle_pause(struct kvm_vcpu *vcpu,
+ struct kvm_run *kvm_run)
+{
+ ktime_t expires;
+ skip_emulated_instruction(vcpu);
+
+ /* Sleep for 1 msec, and hope lock-holder got scheduled */
+ expires = ktime_add_ns(ktime_get(), 1000000UL);
I think this should be much lower, 50-100us. Maybe this should be a
parameter. With 1ms we losing significant cpu time if the congestion
clears.
+ set_current_state(TASK_INTERRUPTIBLE);
+ schedule_hrtimeout(&expires, HRTIMER_MODE_ABS);
+
Please add a tracepoint for this (since it can cause significant change
in behaviour), and move the logic to kvm_main.c. It will be reused by
the AMD implementation, possibly my software spinlock detector,
paravirtualized spinlocks, and hopefully other architectures.
+ return 1;
+}
+
+/*
--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
