Re: [PATCH 7/9] block: Add delay-alert-ms property

Hanna Czenczek Wed, 16 Sep 2026 01:35:23 -0700

On 03.09.26 16:30, Stefan Hajnoczi wrote:

On Mon, Aug 31, 2026 at 03:52:03PM +0200, Hanna Czenczek wrote:

This device property allows setting up an I/O latency threshold for when
to emit a delay QMP event.


Signed-off-by: Hanna Czenczek <[email protected]>
---
  include/hw/block/block.h   |  5 ++++-
  blockdev.c                 | 16 +++++++++++++++-
  hw/block/block.c           |  4 +++-
  tests/qemu-iotests/172.out | 38 ++++++++++++++++++++++++++++++++++++++
  4 files changed, 60 insertions(+), 3 deletions(-)

diff --git a/include/hw/block/block.h b/include/hw/block/block.h
index df941df19f2..e7e401dd303 100644
--- a/include/hw/block/block.h
+++ b/include/hw/block/block.h
@@ -36,6 +36,7 @@ typedef struct BlockConf {
      BlockdevOnError werror;
      uint32_t num_stats_intervals;
      uint32_t *stats_intervals;
+    uint32_t delay_alert_ms;
  } BlockConf;

static inline unsigned int get_physical_block_exp(BlockConf *conf)

@@ -83,7 +84,9 @@ static inline unsigned int get_physical_block_exp(BlockConf 
*conf)
                              _conf.account_failed, ON_OFF_AUTO_AUTO),    \
      DEFINE_PROP_ARRAY("stats-intervals", _state,                        \
                       _conf.num_stats_intervals, _conf.stats_intervals,  \
-                     qdev_prop_uint32, uint32_t)
+                     qdev_prop_uint32, uint32_t),                       \
+    DEFINE_PROP_UINT32("delay-alert-ms", _state, _conf.delay_alert_ms,  \
+                       0)                                               \

The latency histogram feature uses nanoseconds (64-bit integer) whereas
this patch series uses delay-alert-ms (uint32) and a double
floating-point seconds value in the QMP event. Maybe stick to 64-bit
integer nanoseconds everywhere for consistency?

I don’t have technical objections because doing so is easy, of course.Personally, I found nanoseconds really unwieldy to specify here. But Isuppose if @block-latency-histogram-set does the same, then I might as well.


Hanna

#define DEFINE_BLOCK_PROPERTIES(_state, _conf) \

      DEFINE_PROP_DRIVE("drive", _state, _conf.blk),                      \
diff --git a/blockdev.c b/blockdev.c
index 195bac8af01..9c76e89ef38 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -496,6 +496,7 @@ static BlockBackend *blockdev_init(const char *file, QDict 
*bs_opts,
      BlockdevDetectZeroesOptions detect_zeroes =
          BLOCKDEV_DETECT_ZEROES_OPTIONS_OFF;
      const char *throttling_group = NULL;
+    uint64_t delay_alert_ns;

/* Check common options by copying from bs_opts to opts, all other options

       * stay in bs_opts for processing by bdrv_open(). */
@@ -580,6 +581,14 @@ static BlockBackend *blockdev_init(const char *file, QDict 
*bs_opts,

read_only = qemu_opt_get_bool(opts, BDRV_OPT_READ_ONLY, false);+ delay_alert_ns = qemu_opt_get_number(opts, "delay-alert-ms", 0);

+    if (delay_alert_ns > (uint64_t)INT64_MAX / SCALE_MS) {
+        error_setg(errp, "delay-alert-ms must not exceed %" PRId64,
+                   INT64_MAX / SCALE_MS);
+        goto early_err;
+    }
+    delay_alert_ns *= SCALE_MS;
+
      /* init */
      if ((!file || !*file) && !qdict_size(bs_opts)) {
          BlockBackendRootState *blk_rs;
@@ -618,7 +627,7 @@ static BlockBackend *blockdev_init(const char *file, QDict 
*bs_opts,
          bs->detect_zeroes = detect_zeroes;

block_acct_setup(blk_get_stats(blk), account_invalid, account_failed,

-                         NULL, 0, 0, NULL);
+                         NULL, 0, delay_alert_ns, NULL);

if (!parse_stats_intervals(blk_get_stats(blk), interval_list, errp)) {

              blk_unref(blk);
@@ -3753,6 +3762,11 @@ QemuOptsList qemu_common_drive_opts = {
              .type = QEMU_OPT_BOOL,
              .help = "whether to account for failed I/O operations "
                      "in the statistics",
+        },{
+            .name = "delay-alert-ms",
+            .type = QEMU_OPT_NUMBER,
+            .help = "threshold in ms when to emit an I/O operation "
+                    "delay QMP event",
          },
          { /* end of list */ }
      },
diff --git a/hw/block/block.c b/hw/block/block.c
index 19301c6f995..be0ea89cb79 100644
--- a/hw/block/block.c
+++ b/hw/block/block.c
@@ -207,6 +207,7 @@ bool blkconf_apply_backend_options(BlockConf *conf, bool 
readonly,
      BlockBackend *blk = conf->blk;
      BlockdevOnError rerror, werror;
      uint64_t perm, shared_perm;
+    uint64_t delay_alert_ns;
      bool wce;
      int ret;

@@ -249,9 +250,10 @@ bool blkconf_apply_backend_options(BlockConf *conf, bool readonly,

      blk_set_enable_write_cache(blk, wce);
      blk_set_on_error(blk, rerror, werror);

+ delay_alert_ns = (uint64_t)conf->delay_alert_ms * SCALE_MS;

      if (!block_acct_setup(blk_get_stats(blk), conf->account_invalid,
                            conf->account_failed, conf->stats_intervals,
-                          conf->num_stats_intervals, 0, errp)) {
+                          conf->num_stats_intervals, delay_alert_ns, errp)) {
          return false;
      }
      return true;
diff --git a/tests/qemu-iotests/172.out b/tests/qemu-iotests/172.out
index a023cd407de..ea6a1875eb3 100644
--- a/tests/qemu-iotests/172.out
+++ b/tests/qemu-iotests/172.out
@@ -31,6 +31,7 @@ Testing:
                  account-invalid = "auto"
                  account-failed = "auto"
                  stats-intervals = <null>
+                delay-alert-ms = 0 (0x0)
                  drive-type = "288"

@@ -61,6 +62,7 @@ Testing: -fda TEST_DIR/t.qcow2

                  account-invalid = "auto"
                  account-failed = "auto"
                  stats-intervals = <null>
+                delay-alert-ms = 0 (0x0)
                  drive-type = "144"
  floppy0 (NODE_NAME): TEST_DIR/t.qcow2 (qcow2)
      Attached to:      /machine/unattached/device[N]
@@ -98,6 +100,7 @@ Testing: -fdb TEST_DIR/t.qcow2
                  account-invalid = "auto"
                  account-failed = "auto"
                  stats-intervals = <null>
+                delay-alert-ms = 0 (0x0)
                  drive-type = "144"
                dev: floppy, id ""
                  unit = 0 (0x0)
@@ -113,6 +116,7 @@ Testing: -fdb TEST_DIR/t.qcow2
                  account-invalid = "auto"
                  account-failed = "auto"
                  stats-intervals = <null>
+                delay-alert-ms = 0 (0x0)
                  drive-type = "288"
  floppy1 (NODE_NAME): TEST_DIR/t.qcow2 (qcow2)
      Attached to:      /machine/unattached/device[N]
@@ -154,6 +158,7 @@ Testing: -fda TEST_DIR/t.qcow2 -fdb TEST_DIR/t.qcow2.2
                  account-invalid = "auto"
                  account-failed = "auto"
                  stats-intervals = <null>
+                delay-alert-ms = 0 (0x0)
                  drive-type = "144"
                dev: floppy, id ""
                  unit = 0 (0x0)
@@ -169,6 +174,7 @@ Testing: -fda TEST_DIR/t.qcow2 -fdb TEST_DIR/t.qcow2.2
                  account-invalid = "auto"
                  account-failed = "auto"
                  stats-intervals = <null>
+                delay-alert-ms = 0 (0x0)
                  drive-type = "144"
  floppy0 (NODE_NAME): TEST_DIR/t.qcow2 (qcow2)
      Attached to:      /machine/unattached/device[N]
@@ -211,6 +217,7 @@ Testing: -fdb
                  account-invalid = "auto"
                  account-failed = "auto"
                  stats-intervals = <null>
+                delay-alert-ms = 0 (0x0)
                  drive-type = "288"
                dev: floppy, id ""
                  unit = 0 (0x0)
@@ -226,6 +233,7 @@ Testing: -fdb
                  account-invalid = "auto"
                  account-failed = "auto"
                  stats-intervals = <null>
+                delay-alert-ms = 0 (0x0)
                  drive-type = "288"

@@ -256,6 +264,7 @@ Testing: -drive if=floppy,file=TEST_DIR/t.qcow2

                  account-invalid = "auto"
                  account-failed = "auto"
                  stats-intervals = <null>
+                delay-alert-ms = 0 (0x0)
                  drive-type = "144"
  floppy0 (NODE_NAME): TEST_DIR/t.qcow2 (qcow2)
      Attached to:      /machine/unattached/device[N]
@@ -293,6 +302,7 @@ Testing: -drive if=floppy,file=TEST_DIR/t.qcow2,index=1
                  account-invalid = "auto"
                  account-failed = "auto"
                  stats-intervals = <null>
+                delay-alert-ms = 0 (0x0)
                  drive-type = "144"
                dev: floppy, id ""
                  unit = 0 (0x0)
@@ -308,6 +318,7 @@ Testing: -drive if=floppy,file=TEST_DIR/t.qcow2,index=1
                  account-invalid = "auto"
                  account-failed = "auto"
                  stats-intervals = <null>
+                delay-alert-ms = 0 (0x0)
                  drive-type = "288"
  floppy1 (NODE_NAME): TEST_DIR/t.qcow2 (qcow2)
      Attached to:      /machine/unattached/device[N]
@@ -349,6 +360,7 @@ Testing: -drive if=floppy,file=TEST_DIR/t.qcow2 -drive 
if=floppy,file=TEST_DIR/t
                  account-invalid = "auto"
                  account-failed = "auto"
                  stats-intervals = <null>
+                delay-alert-ms = 0 (0x0)
                  drive-type = "144"
                dev: floppy, id ""
                  unit = 0 (0x0)
@@ -364,6 +376,7 @@ Testing: -drive if=floppy,file=TEST_DIR/t.qcow2 -drive 
if=floppy,file=TEST_DIR/t
                  account-invalid = "auto"
                  account-failed = "auto"
                  stats-intervals = <null>
+                delay-alert-ms = 0 (0x0)
                  drive-type = "144"
  floppy0 (NODE_NAME): TEST_DIR/t.qcow2 (qcow2)
      Attached to:      /machine/unattached/device[N]
@@ -409,6 +422,7 @@ Testing: -drive if=none,file=TEST_DIR/t.qcow2 -device 
floppy,drive=none0
                  account-invalid = "auto"
                  account-failed = "auto"
                  stats-intervals = <null>
+                delay-alert-ms = 0 (0x0)
                  drive-type = "144"
  none0 (NODE_NAME): TEST_DIR/t.qcow2 (qcow2)
      Attached to:      /machine/peripheral-anon/device[N]
@@ -446,6 +460,7 @@ Testing: -drive if=none,file=TEST_DIR/t.qcow2 -device 
floppy,drive=none0,unit=1
                  account-invalid = "auto"
                  account-failed = "auto"
                  stats-intervals = <null>
+                delay-alert-ms = 0 (0x0)
                  drive-type = "144"
  none0 (NODE_NAME): TEST_DIR/t.qcow2 (qcow2)
      Attached to:      /machine/peripheral-anon/device[N]
@@ -483,6 +498,7 @@ Testing: -drive if=none,file=TEST_DIR/t.qcow2 -drive 
if=none,file=TEST_DIR/t.qco
                  account-invalid = "auto"
                  account-failed = "auto"
                  stats-intervals = <null>
+                delay-alert-ms = 0 (0x0)
                  drive-type = "144"
                dev: floppy, id ""
                  unit = 0 (0x0)
@@ -498,6 +514,7 @@ Testing: -drive if=none,file=TEST_DIR/t.qcow2 -drive 
if=none,file=TEST_DIR/t.qco
                  account-invalid = "auto"
                  account-failed = "auto"
                  stats-intervals = <null>
+                delay-alert-ms = 0 (0x0)
                  drive-type = "144"
  none0 (NODE_NAME): TEST_DIR/t.qcow2 (qcow2)
      Attached to:      /machine/peripheral-anon/device[N]
@@ -549,6 +566,7 @@ Testing: -fda TEST_DIR/t.qcow2 -drive 
if=none,file=TEST_DIR/t.qcow2.2 -device fl
                  account-invalid = "auto"
                  account-failed = "auto"
                  stats-intervals = <null>
+                delay-alert-ms = 0 (0x0)
                  drive-type = "144"
                dev: floppy, id ""
                  unit = 0 (0x0)
@@ -564,6 +582,7 @@ Testing: -fda TEST_DIR/t.qcow2 -drive 
if=none,file=TEST_DIR/t.qcow2.2 -device fl
                  account-invalid = "auto"
                  account-failed = "auto"
                  stats-intervals = <null>
+                delay-alert-ms = 0 (0x0)
                  drive-type = "144"
  floppy0 (NODE_NAME): TEST_DIR/t.qcow2 (qcow2)
      Attached to:      /machine/unattached/device[N]
@@ -606,6 +625,7 @@ Testing: -fda TEST_DIR/t.qcow2 -drive 
if=none,file=TEST_DIR/t.qcow2.2 -device fl
                  account-invalid = "auto"
                  account-failed = "auto"
                  stats-intervals = <null>
+                delay-alert-ms = 0 (0x0)
                  drive-type = "144"
                dev: floppy, id ""
                  unit = 0 (0x0)
@@ -621,6 +641,7 @@ Testing: -fda TEST_DIR/t.qcow2 -drive 
if=none,file=TEST_DIR/t.qcow2.2 -device fl
                  account-invalid = "auto"
                  account-failed = "auto"
                  stats-intervals = <null>
+                delay-alert-ms = 0 (0x0)
                  drive-type = "144"
  floppy0 (NODE_NAME): TEST_DIR/t.qcow2 (qcow2)
      Attached to:      /machine/unattached/device[N]
@@ -663,6 +684,7 @@ Testing: -fdb TEST_DIR/t.qcow2 -drive 
if=none,file=TEST_DIR/t.qcow2.2 -device fl
                  account-invalid = "auto"
                  account-failed = "auto"
                  stats-intervals = <null>
+                delay-alert-ms = 0 (0x0)
                  drive-type = "144"
                dev: floppy, id ""
                  unit = 1 (0x1)
@@ -678,6 +700,7 @@ Testing: -fdb TEST_DIR/t.qcow2 -drive 
if=none,file=TEST_DIR/t.qcow2.2 -device fl
                  account-invalid = "auto"
                  account-failed = "auto"
                  stats-intervals = <null>
+                delay-alert-ms = 0 (0x0)
                  drive-type = "144"
  floppy1 (NODE_NAME): TEST_DIR/t.qcow2 (qcow2)
      Attached to:      /machine/unattached/device[N]
@@ -720,6 +743,7 @@ Testing: -fdb TEST_DIR/t.qcow2 -drive 
if=none,file=TEST_DIR/t.qcow2.2 -device fl
                  account-invalid = "auto"
                  account-failed = "auto"
                  stats-intervals = <null>
+                delay-alert-ms = 0 (0x0)
                  drive-type = "144"
                dev: floppy, id ""
                  unit = 1 (0x1)
@@ -735,6 +759,7 @@ Testing: -fdb TEST_DIR/t.qcow2 -drive 
if=none,file=TEST_DIR/t.qcow2.2 -device fl
                  account-invalid = "auto"
                  account-failed = "auto"
                  stats-intervals = <null>
+                delay-alert-ms = 0 (0x0)
                  drive-type = "144"
  floppy1 (NODE_NAME): TEST_DIR/t.qcow2 (qcow2)
      Attached to:      /machine/unattached/device[N]
@@ -786,6 +811,7 @@ Testing: -drive if=floppy,file=TEST_DIR/t.qcow2 -drive 
if=none,file=TEST_DIR/t.q
                  account-invalid = "auto"
                  account-failed = "auto"
                  stats-intervals = <null>
+                delay-alert-ms = 0 (0x0)
                  drive-type = "144"
                dev: floppy, id ""
                  unit = 0 (0x0)
@@ -801,6 +827,7 @@ Testing: -drive if=floppy,file=TEST_DIR/t.qcow2 -drive 
if=none,file=TEST_DIR/t.q
                  account-invalid = "auto"
                  account-failed = "auto"
                  stats-intervals = <null>
+                delay-alert-ms = 0 (0x0)
                  drive-type = "144"
  floppy0 (NODE_NAME): TEST_DIR/t.qcow2 (qcow2)
      Attached to:      /machine/unattached/device[N]
@@ -843,6 +870,7 @@ Testing: -drive if=floppy,file=TEST_DIR/t.qcow2 -drive 
if=none,file=TEST_DIR/t.q
                  account-invalid = "auto"
                  account-failed = "auto"
                  stats-intervals = <null>
+                delay-alert-ms = 0 (0x0)
                  drive-type = "144"
                dev: floppy, id ""
                  unit = 0 (0x0)
@@ -858,6 +886,7 @@ Testing: -drive if=floppy,file=TEST_DIR/t.qcow2 -drive 
if=none,file=TEST_DIR/t.q
                  account-invalid = "auto"
                  account-failed = "auto"
                  stats-intervals = <null>
+                delay-alert-ms = 0 (0x0)
                  drive-type = "144"
  floppy0 (NODE_NAME): TEST_DIR/t.qcow2 (qcow2)
      Attached to:      /machine/unattached/device[N]
@@ -906,6 +935,7 @@ Testing: -drive if=none,file=TEST_DIR/t.qcow2 -global 
floppy.drive=none0 -device
                  account-invalid = "auto"
                  account-failed = "auto"
                  stats-intervals = <null>
+                delay-alert-ms = 0 (0x0)
                  drive-type = "144"
  none0 (NODE_NAME): TEST_DIR/t.qcow2 (qcow2)
      Attached to:      /machine/peripheral-anon/device[N]
@@ -973,6 +1003,7 @@ Testing: -device floppy
                  account-invalid = "auto"
                  account-failed = "auto"
                  stats-intervals = <null>
+                delay-alert-ms = 0 (0x0)
                  drive-type = "288"

Testing: -device floppy,drive-type=120

@@ -1000,6 +1031,7 @@ Testing: -device floppy,drive-type=120
                  account-invalid = "auto"
                  account-failed = "auto"
                  stats-intervals = <null>
+                delay-alert-ms = 0 (0x0)
                  drive-type = "120"

Testing: -device floppy,drive-type=144

@@ -1027,6 +1059,7 @@ Testing: -device floppy,drive-type=144
                  account-invalid = "auto"
                  account-failed = "auto"
                  stats-intervals = <null>
+                delay-alert-ms = 0 (0x0)
                  drive-type = "144"

Testing: -device floppy,drive-type=288

@@ -1054,6 +1087,7 @@ Testing: -device floppy,drive-type=288
                  account-invalid = "auto"
                  account-failed = "auto"
                  stats-intervals = <null>
+                delay-alert-ms = 0 (0x0)
                  drive-type = "288"

@@ -1084,6 +1118,7 @@ Testing: -drive if=none,file=TEST_DIR/t.qcow2 -device floppy,drive=none0,drive-t

                  account-invalid = "auto"
                  account-failed = "auto"
                  stats-intervals = <null>
+                delay-alert-ms = 0 (0x0)
                  drive-type = "120"
  none0 (NODE_NAME): TEST_DIR/t.qcow2 (qcow2)
      Attached to:      /machine/peripheral-anon/device[N]
@@ -1121,6 +1156,7 @@ Testing: -drive if=none,file=TEST_DIR/t.qcow2 -device 
floppy,drive=none0,drive-t
                  account-invalid = "auto"
                  account-failed = "auto"
                  stats-intervals = <null>
+                delay-alert-ms = 0 (0x0)
                  drive-type = "288"
  none0 (NODE_NAME): TEST_DIR/t.qcow2 (qcow2)
      Attached to:      /machine/peripheral-anon/device[N]
@@ -1161,6 +1197,7 @@ Testing: -drive if=none,file=TEST_DIR/t.qcow2 -device 
floppy,drive=none0,logical
                  account-invalid = "auto"
                  account-failed = "auto"
                  stats-intervals = <null>
+                delay-alert-ms = 0 (0x0)
                  drive-type = "144"
  none0 (NODE_NAME): TEST_DIR/t.qcow2 (qcow2)
      Attached to:      /machine/peripheral-anon/device[N]
@@ -1198,6 +1235,7 @@ Testing: -drive if=none,file=TEST_DIR/t.qcow2 -device 
floppy,drive=none0,physica
                  account-invalid = "auto"
                  account-failed = "auto"
                  stats-intervals = <null>
+                delay-alert-ms = 0 (0x0)
                  drive-type = "144"
  none0 (NODE_NAME): TEST_DIR/t.qcow2 (qcow2)
      Attached to:      /machine/peripheral-anon/device[N]
--
2.55.0

Re: [PATCH 7/9] block: Add delay-alert-ms property

Reply via email to