MINOR: task: add one extra tasklet class: TL_HEAVY
This class will be used exclusively for heavy processing tasklets. It
will be cleaner than mixing them with the bulk ones. For now it's
allocated ~1% of the CPU bandwidth.
The largest part of the patch consists in re-arranging the fields in the
task_per_thread structure to preserve a clean alignment with one more
list head. Since we're now forced to increase the struct past a second
cache line, it now uses 4 cache lines (for easy multiplying) with the
first two ones being exclusively used by local operations and the third
one mostly by atomic operations. Interestingly, this better arrangement
causes less stress and reduced the response time by 8 microseconds at
1 million requests per second.
diff --git a/src/task.c b/src/task.c
index 1cb8352..1b1738d 100644
--- a/src/task.c
+++ b/src/task.c
@@ -635,6 +635,7 @@
[TL_URGENT] = 64, // ~50% of CPU bandwidth for I/O
[TL_NORMAL] = 48, // ~37% of CPU bandwidth for tasks
[TL_BULK] = 16, // ~13% of CPU bandwidth for self-wakers
+ [TL_HEAVY] = 1, // never more than 1 heavy task at once
};
unsigned int max[TL_CLASSES]; // max to be run per class
unsigned int max_total; // sum of max above
@@ -673,6 +674,14 @@
if ((tt->tl_class_mask & (1 << TL_BULK)))
max[TL_BULK] = default_weights[TL_BULK];
+ /* heavy tasks are processed only once and never refilled in a
+ * call round.
+ */
+ if ((tt->tl_class_mask & (1 << TL_HEAVY)))
+ max[TL_HEAVY] = default_weights[TL_HEAVY];
+ else
+ max[TL_HEAVY] = 0;
+
/* Now compute a fair share of the weights. Total may slightly exceed
* 100% due to rounding, this is not a problem. Note that while in
* theory the sum cannot be NULL as we cannot get there without tasklets
@@ -681,7 +690,7 @@
* a first MT_LIST_ISEMPTY() to succeed for thread_has_task() and the
* one above to finally fail. This is extremely rare and not a problem.
*/
- max_total = max[TL_URGENT] + max[TL_NORMAL] + max[TL_BULK];
+ max_total = max[TL_URGENT] + max[TL_NORMAL] + max[TL_BULK] + max[TL_HEAVY];
if (!max_total)
return;
@@ -881,7 +890,7 @@
/* perform minimal intializations */
static void init_task()
{
- int i;
+ int i, q;
#ifdef USE_THREAD
memset(&timers, 0, sizeof(timers));
@@ -889,9 +898,8 @@
#endif
memset(&task_per_thread, 0, sizeof(task_per_thread));
for (i = 0; i < MAX_THREADS; i++) {
- LIST_INIT(&task_per_thread[i].tasklets[TL_URGENT]);
- LIST_INIT(&task_per_thread[i].tasklets[TL_NORMAL]);
- LIST_INIT(&task_per_thread[i].tasklets[TL_BULK]);
+ for (q = 0; q < TL_CLASSES; q++)
+ LIST_INIT(&task_per_thread[i].tasklets[q]);
MT_LIST_INIT(&task_per_thread[i].shared_tasklet_list);
}
}