[Qemu-devel] [RFC PATCH V3 6/6] monitor: Add drift info to 'info jit'

[Sebastian Tanase]

Show in 'info jit' the current delay between the host clock
and the guest clock. In addition, print the maximum advance
and delay of the guest compared to the host.

Signed-off-by: Sebastian Tanase <address@hidden>
Tested-by: Camille Bégué <address@hidden>
---
 cpu-exec.c            | 61 +++++++++++++++++++++++++++++++++++----------------
 cpus.c                | 17 ++++++++++++++
 include/qemu-common.h |  5 +++++
 monitor.c             |  1 +
 4 files changed, 65 insertions(+), 19 deletions(-)

diff --git a/cpu-exec.c b/cpu-exec.c
index 4a4533d..06809f2 100644
--- a/cpu-exec.c
+++ b/cpu-exec.c
@@ -104,25 +104,18 @@ static void init_delay_params(SyncClocks *sc,
                               int64_t realtime_clock_value,
                               const CPUState *cpu)
 {
-    static int64_t clocks_offset = -1;
-    int64_t virtual_clock_value;
     if (!icount_align_option) {
         return;
     }
-    /* On x86 target architecture, the PIT reset function (called
-       by qemu_system_reset) will end up calling qemu_clock_warp
-       and then icount_warp_rt changing vm_clock_warp_start from 0 (initial
-       value) to -1. This in turn will make us skip the initial offset
-       between the real and virtual clocks (initially virtual clock is 0).
-       Therefore we impose that the first time we run the cpu
-       the host and virtual clocks should be aligned; we don't alter any of
-       the clocks, we just calculate the difference between them. */
-    virtual_clock_value = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
-    if (clocks_offset == -1) {
-        clocks_offset = realtime_clock_value - virtual_clock_value;
-    }
-    sc->diff_clk = virtual_clock_value - realtime_clock_value + clocks_offset;
+    sc->diff_clk = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) -
+                   realtime_clock_value + clocks_offset;
     sc->original_instr_counter = cpu->icount_extra + cpu->icount_decr.u16.low;
+    if (sc->diff_clk < max_delay) {
+        max_delay = sc->diff_clk;
+    }
+    if (sc->diff_clk > max_advance) {
+        max_advance = sc->diff_clk;
+    }
 }
 static void print_delay(InformDelay *indl, int64_t diff_clk)
 {
@@ -160,10 +153,32 @@ static void init_inform(InformDelay *indl, int64_t 
realtime_clock_value)
 
 static void compute_value_of_rtc(int64_t *realtime_clock_value)
 {
-    if (!icount_align_option) {
-        return;
+    /* When using align, we use every time the value of the host clock
+       whereas when not using align, we only need it once to calculate
+       the offset between the host and virtual clocks. We then use this
+       value to correctly print the delay between the 2 clocks when using
+       "info jit" in the monitor. */
+    if (icount_align_option) {
+        *realtime_clock_value = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
+    } else if (*realtime_clock_value == 0) {
+        *realtime_clock_value = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
+    }
+}
+
+static void compute_clocks_offset(int64_t realtime_clock_value)
+{
+    /* On x86 target architecture, the PIT reset function (called
+       by qemu_system_reset) will end up calling qemu_clock_warp
+       and then icount_warp_rt changing vm_clock_warp_start from 0 (initial
+       value) to -1. This in turn will make us skip the initial offset
+       between the real and virtual clocks (initially virtual clock is 0).
+       Therefore we suppose that the first time we run the cpu
+       the host and virtual clocks should be aligned; we don't alter any of
+       the clocks, we just calculate the difference between them. */
+    if (clocks_offset == -1) {
+        clocks_offset = realtime_clock_value -
+                        qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
     }
-    *realtime_clock_value = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
 }
 #else
 /* We don't use the align feature for User emulation
@@ -189,6 +204,10 @@ static void init_inform(InformDelay *indl, int64_t 
realtime_clock_value)
 static void compute_value_of_rtc(int64_t *realtime_clock_value)
 {
 }
+
+static void compute_clocks_offset(int64_t realtime_clock_value)
+{
+}
 #endif /* CONFIG USER ONLY */
 
 void cpu_loop_exit(CPUState *cpu)
@@ -396,7 +415,7 @@ int cpu_exec(CPUArchState *env)
     uint8_t *tc_ptr;
     uintptr_t next_tb;
     /* Delay algorithm */
-    int64_t realtime_clock_value;
+    static int64_t realtime_clock_value;
     static SyncClocks sc = {
         .init_delay = init_delay_params,
         .perform_align = align_clocks
@@ -465,6 +484,10 @@ int cpu_exec(CPUArchState *env)
     /* Calculating the realtime is expensive so we do it once here
        and then pass this value around. */
     compute_value_of_rtc(&realtime_clock_value);
+    /* We calculate the clocks_offset here, the very first time
+       we run the cpu; we do it here because it gives us the best
+       accuracy. */
+    compute_clocks_offset(realtime_clock_value);
     /* Calculate difference between guest clock and host clock.
        This delay includes the delay of the last cycle, so
        what we have to do is sleep until it is 0. As for the
diff --git a/cpus.c b/cpus.c
index 312c2ee..9947d40 100644
--- a/cpus.c
+++ b/cpus.c
@@ -64,6 +64,9 @@
 #endif /* CONFIG_LINUX */
 
 static CPUState *next_cpu;
+int64_t clocks_offset = -1;
+int64_t max_delay;
+int64_t max_advance;
 
 bool cpu_is_stopped(CPUState *cpu)
 {
@@ -1512,3 +1515,17 @@ void qmp_inject_nmi(Error **errp)
     error_set(errp, QERR_UNSUPPORTED);
 #endif
 }
+
+void dump_drift_info(FILE *f, fprintf_function cpu_fprintf)
+{
+    cpu_fprintf(f, "Host - Guest clock  %ld(ms)\n",
+                (qemu_clock_get_ns(QEMU_CLOCK_REALTIME) - clocks_offset -
+                 qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL))/SCALE_MS);
+    if (icount_align_option) {
+        cpu_fprintf(f, "Max guest delay     %ld(ms)\n", -max_delay/SCALE_MS);
+        cpu_fprintf(f, "Max guest advance   %ld(ms)\n", max_advance/SCALE_MS);
+    } else {
+        cpu_fprintf(f, "Max guest delay     NA\n");
+        cpu_fprintf(f, "Max guest advance   NA\n");
+    }
+}
diff --git a/include/qemu-common.h b/include/qemu-common.h
index f568635..f86b27b 100644
--- a/include/qemu-common.h
+++ b/include/qemu-common.h
@@ -110,6 +110,11 @@ void configure_icount(QemuOpts *opts, Error **errp);
 extern int use_icount;
 extern int icount_time_shift;
 extern int icount_align_option;
+extern int64_t clocks_offset;
+/* drift information for info jit command */
+extern int64_t max_delay;
+extern int64_t max_advance;
+void dump_drift_info(FILE *f, fprintf_function cpu_fprintf);
 
 #include "qemu/osdep.h"
 #include "qemu/bswap.h"
diff --git a/monitor.c b/monitor.c
index 799131b..23c5534 100644
--- a/monitor.c
+++ b/monitor.c
@@ -1047,6 +1047,7 @@ static void do_info_registers(Monitor *mon, const QDict 
*qdict)
 static void do_info_jit(Monitor *mon, const QDict *qdict)
 {
     dump_exec_info((FILE *)mon, monitor_fprintf);
+    dump_drift_info((FILE *)mon, monitor_fprintf);
 }
 
 static void do_info_history(Monitor *mon, const QDict *qdict)
-- 
2.0.0.rc2