[Qemu-devel] [PATCH] block/throttle: Use host clock type

[Fam Zheng <famz@redhat.com>]

Throttle timers won't make any progress when VCPU is not running, which
is prone to stall the request queue in cases like utils, qtest,
suspending, and live migration, unless carefully handled. What we do now
is crude. For example in bdrv_drain_all, requests are resumed
immediately without consulting throttling timer. Unfortunately
bdrv_drain_all is so widely used that there may be too many holes that
guest could bypass throttling.

If we use the host clock, we can just trust the nested poll when waiting
for requests.

Signed-off-by: Fam Zheng <famz@redhat.com>
---
 block.c               |  2 +-
 tests/test-throttle.c | 14 +++++++-------
 2 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/block.c b/block.c
index 191a847..11f9065 100644
--- a/block.c
+++ b/block.c
@@ -184,7 +184,7 @@ void bdrv_io_limits_enable(BlockDriverState *bs)
     assert(!bs->io_limits_enabled);
     throttle_init(&bs->throttle_state,
                   bdrv_get_aio_context(bs),
-                  QEMU_CLOCK_VIRTUAL,
+                  QEMU_CLOCK_HOST,
                   bdrv_throttle_read_timer_cb,
                   bdrv_throttle_write_timer_cb,
                   bs);
diff --git a/tests/test-throttle.c b/tests/test-throttle.c
index d8ba415..1fb1792 100644
--- a/tests/test-throttle.c
+++ b/tests/test-throttle.c
@@ -107,11 +107,11 @@ static void test_init(void)
     memset(&ts, 1, sizeof(ts));
 
     /* init the structure */
-    throttle_init(&ts, ctx, QEMU_CLOCK_VIRTUAL,
+    throttle_init(&ts, ctx, QEMU_CLOCK_HOST,
                   read_timer_cb, write_timer_cb, &ts);
 
     /* check initialized fields */
-    g_assert(ts.clock_type == QEMU_CLOCK_VIRTUAL);
+    g_assert(ts.clock_type == QEMU_CLOCK_HOST);
     g_assert(ts.timers[0]);
     g_assert(ts.timers[1]);
 
@@ -130,7 +130,7 @@ static void test_init(void)
 static void test_destroy(void)
 {
     int i;
-    throttle_init(&ts, ctx, QEMU_CLOCK_VIRTUAL,
+    throttle_init(&ts, ctx, QEMU_CLOCK_HOST,
                   read_timer_cb, write_timer_cb, &ts);
     throttle_destroy(&ts);
     for (i = 0; i < 2; i++) {
@@ -170,7 +170,7 @@ static void test_config_functions(void)
 
     orig_cfg.op_size = 1;
 
-    throttle_init(&ts, ctx, QEMU_CLOCK_VIRTUAL,
+    throttle_init(&ts, ctx, QEMU_CLOCK_HOST,
                   read_timer_cb, write_timer_cb, &ts);
     /* structure reset by throttle_init previous_leak should be null */
     g_assert(!ts.previous_leak);
@@ -330,7 +330,7 @@ static void test_have_timer(void)
     g_assert(!throttle_have_timer(&ts));
 
     /* init the structure */
-    throttle_init(&ts, ctx, QEMU_CLOCK_VIRTUAL,
+    throttle_init(&ts, ctx, QEMU_CLOCK_HOST,
                   read_timer_cb, write_timer_cb, &ts);
 
     /* timer set by init should return true */
@@ -345,7 +345,7 @@ static void test_detach_attach(void)
     memset(&ts, 0, sizeof(ts));
 
     /* init the structure */
-    throttle_init(&ts, ctx, QEMU_CLOCK_VIRTUAL,
+    throttle_init(&ts, ctx, QEMU_CLOCK_HOST,
                   read_timer_cb, write_timer_cb, &ts);
 
     /* timer set by init should return true */
@@ -387,7 +387,7 @@ static bool do_test_accounting(bool is_ops, /* are we testing bps or ops */
 
     cfg.op_size = op_size;
 
-    throttle_init(&ts, ctx, QEMU_CLOCK_VIRTUAL,
+    throttle_init(&ts, ctx, QEMU_CLOCK_HOST,
                   read_timer_cb, write_timer_cb, &ts);
     throttle_config(&ts, &cfg);
 
-- 
1.9.3