This
is the kernel side code to implement a virtual irq that gets sent when
the xen trace buffers become half-full. This allows userland tools such
as xentrace and xenmon to avoid polling for new trace records. A future
patch will include support for this in XenMon, along with various other
enhancements and bug fixes.
This patch has been tested on x86, x86-64, and x86 SMP machines.
Rob Gardner
# HG changeset patch
# User
rob.gardner@xxxxxx
# Node ID 8e3d7bce3b29841a323056defacdb1181c252282
# Parent f0e14b4e535c7d99c56c286384b0d512c5220884
Added trace buffer virtual irq to implement non-polling trace record
access
Signed-off-by: Rob Gardner
<rob.gardner@xxxxxx>
diff -r f0e14b4e535c -r 8e3d7bce3b29 xen/common/trace.c
--- a/xen/common/trace.c Thu Mar 30 13:37:22 2006
+++ b/xen/common/trace.c Fri Mar 31 17:33:04 2006
@@ -27,6 +27,8 @@
#include <xen/smp.h>
#include <xen/trace.h>
#include <xen/errno.h>
+#include <xen/event.h>
+#include <xen/softirq.h>
#include <xen/init.h>
#include <asm/atomic.h>
#include <public/dom0_ops.h>
@@ -40,6 +42,10 @@
static struct t_rec *t_recs[NR_CPUS];
static int nr_recs;
+/* High water mark for trace buffers; */
+/* Send virtual interrupt when buffer level reaches this point */
+static int t_buf_highwater;
+
/* a flag recording whether initialization has been done */
/* or more properly, if the tbuf subsystem is enabled right now */
int tb_init_done;
@@ -49,6 +55,13 @@
/* which tracing events are enabled */
static u32 tb_event_mask = TRC_ALL;
+
+
+static void trace_notify_guest(void)
+{
+ send_guest_virq(dom0->vcpu[0], VIRQ_TBUF);
+}
+
/**
* alloc_trace_bufs - performs initialization of the per-cpu trace
buffers.
@@ -93,6 +106,8 @@
t_recs[i] = (struct t_rec *)(buf + 1);
}
+ t_buf_highwater = nr_recs >> 1; /* 50% high water */
+ open_softirq(TRACE_SOFTIRQ, trace_notify_guest);
return 0;
}
@@ -228,6 +243,7 @@
struct t_buf *buf;
struct t_rec *rec;
unsigned long flags;
+ static uint32_t last_virq_sent = 0;
BUG_ON(!tb_init_done);
@@ -272,6 +288,18 @@
buf->prod++;
local_irq_restore(flags);
+
+ /*
+ * Notify trace buffer consumer that we've reached the high water
+ * point. We don't want to repeatedly send virq's, so remember
+ * when we sent the last one.
+ *
+ */
+ if ( ((buf->prod - buf->cons) >= t_buf_highwater)
+ && (buf->cons > last_virq_sent)) {
+ last_virq_sent = buf->cons;
+ raise_softirq(TRACE_SOFTIRQ);
+ }
}
/*
diff -r f0e14b4e535c -r 8e3d7bce3b29 xen/include/public/xen.h
--- a/xen/include/public/xen.h Thu Mar 30 13:37:22 2006
+++ b/xen/include/public/xen.h Fri Mar 31 17:33:04 2006
@@ -71,6 +71,7 @@
#define VIRQ_CONSOLE 2 /* (DOM0) Bytes received on emergency
console. */
#define VIRQ_DOM_EXC 3 /* (DOM0) Exceptional event for some
domain. */
#define VIRQ_DEBUGGER 6 /* (DOM0) A domain has paused for
debugging. */
+#define VIRQ_TBUF 7 /* (DOM0) Trace buffer has records
available */
#define NR_VIRQS 8
/*
diff -r f0e14b4e535c -r 8e3d7bce3b29 xen/include/xen/softirq.h
--- a/xen/include/xen/softirq.h Thu Mar 30 13:37:22 2006
+++ b/xen/include/xen/softirq.h Fri Mar 31 17:33:04 2006
@@ -9,7 +9,8 @@
#define NMI_SOFTIRQ 4
#define PAGE_SCRUB_SOFTIRQ 5
#define DOMAIN_SHUTDOWN_FINALISE_SOFTIRQ 6
-#define NR_SOFTIRQS 7
+#define TRACE_SOFTIRQ 7
+#define NR_SOFTIRQS 8
#ifndef __ASSEMBLY__
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