On 03.09.26 17:08, Stefan Hajnoczi wrote:
On Mon, Aug 31, 2026 at 03:52:04PM +0200, Hanna Czenczek wrote:
I am not quite sure why `latency_ns` is overridden by a fixed value in
qtest mode because personally, I find it much better if I can
individually change requests' latency by modifying the qtest clock.
It looks like tests/qemu-iotests/136 relies on a hardcoded constant so
it can check min/max/avg against known values.
But I'm not going to change existing behavior for the histogram and
such, so I will just move this override after the latency has been
evaluated regarding a potential BLOCK_IO_DELAY event.
That's fine if you aren't taking the same testing approach as
tests/qemu-iotests/136. I think the benefit of hardcoding the value for
testing is that it would become possible to trigger the latency
threshold without worrying about timing in the test environment.
FWIW, as far as I understand, in qtest mode, `clock_type` is
`QEMU_CLOCK_VIRTUAL`, so it is not dependent on the test environment
anyway, but on the qtest clock. That’s why I don’t understand the fixed
latency value, but maybe it was just easier this way for 136 because
this way it does not have to do a clock_step for each request.
Hanna
Signed-off-by: Hanna Czenczek <[email protected]>
---
block/accounting.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/block/accounting.c b/block/accounting.c
index debf1924455..223becd2e04 100644
--- a/block/accounting.c
+++ b/block/accounting.c
@@ -271,10 +271,6 @@ static void block_account_one_io(BlockAcctStats *stats,
BlockAcctCookie *cookie,
int64_t time_ns = qemu_clock_get_ns(clock_type);
int64_t latency_ns = time_ns - cookie->start_time_ns;
- if (qtest_enabled()) {
- latency_ns = qtest_latency_ns;
- }
-
assert(cookie->type < BLOCK_MAX_IOTYPE);
if (cookie->type == BLOCK_ACCT_NONE) {
@@ -292,6 +288,10 @@ static void block_account_one_io(BlockAcctStats *stats,
BlockAcctCookie *cookie,
cookie->bytes);
}
+ if (qtest_enabled()) {
+ latency_ns = qtest_latency_ns;
+ }
+
WITH_QEMU_LOCK_GUARD(&stats->lock) {
if (failed) {
stats->failed_ops[cookie->type]++;
--
2.55.0
