On 1/18/24 10:04, Jens Axboe wrote:
If we're entering request dispatch but someone else is already
dispatching, then just skip this dispatch. We know IO is inflight and
this will trigger another dispatch event for any completion. This will
potentially cause slightly lower queue depth for contended cases, but
those are slowed down anyway and this should not cause an issue.
Shouldn't a performance optimization patch include numbers that show by
how much that patch improves the performance of different workloads?
struct deadline_data {
/*
* run time data
*/
+ struct {
+ spinlock_t lock;
+ spinlock_t zone_lock;
+ } ____cacheline_aligned_in_smp;
Is ____cacheline_aligned_in_smp useful here? struct deadline_data
is not embedded in any other data structure but is allocated with
kzalloc_node().
+ /*
+ * If someone else is already dispatching, skip this one. This will
+ * defer the next dispatch event to when something completes, and could
+ * potentially lower the queue depth for contended cases.
+ */
+ if (test_bit(DD_DISPATCHING, &dd->run_state) ||
+ test_and_set_bit(DD_DISPATCHING, &dd->run_state))
+ return NULL;
+
The above code behaves similar to spin_trylock(). Has it been considered
to use spin_trylock() instead?
Thanks,
Bart.
