Hello, Tao.
On Sat, 03 Oct 2026 20:40:43 +0800, Tao Cui wrote:
> + dev = getenv("IOCOST_TEST_DEV");
Nothing in the tree sets IOCOST_TEST_DEV, so both tests always skip in CI.
The null_blk instance the v11 removal test creates could serve these two
as well.
> + if (ASSERT_OK(err, "readback"))
> + ASSERT_EQ(strcmp(model, "bpf"), 0, "model_bpf");
ASSERT_STREQ() prints both strings on failure.
> + bpf_link__destroy(skel->links.iocost_2x);
> + /* cleared, or the skeleton destroy below detaches again */
> + skel->links.iocost_2x = NULL;
Without clearing, the skeleton destroy would call bpf_link__destroy() on
the freed link. It wouldn't detach again.
> + * The cursor handling follows the builtin: a zero cursor means "no
> + * previous IO", and the cursor is advanced for bios the builtin
> + * prices (READ/WRITE with a non-zero size; the builtin skips the
> + * whole update when the cost is zero), so flushes and discards
> + * leave it alone and long merged streams do not drift past the
> + * 16MB seek threshold.
The model advances the cursor for every merged READ or WRITE bio.
ioc_rqos_merge() only moves it on a back merge into the request ending at
the cursor, so a front merge leaves the builtin's cursor alone and moves
the model's.
> + } else {
> + base = randio;
> + for (i = 1; i < NSLOTS; i++) {
> + if (s->stamp[i] < s->stamp[victim])
> + victim = i;
> + }
A merged bio which matches no slot, e.g. a front merge or a merge into
another stream's request, takes the LRU slot and can evict a live stream.
Maybe skip the slot replacement for IOCOST_COST_F_MERGE?
Thanks.
--
tejun
