Messages in this thread | | | Date | Thu, 14 Jul 2005 22:38:55 +0200 | From | Johannes Stezenbach <> | Subject | Re: [PATCH] i386: Selectable Frequency of the Timer Interrupt |
| |
On Thu, Jul 14, 2005 Linus Torvalds wrote: > In other words, the _right_ way to do this is literally > > unsigned long timeout = jiffies + HZ/2; > for (;;) { > if (ready()) > return 0; > if (time_after(timeout, jiffies)) > break; > msleep(10); > } > > which is unquestionably more complex, yes, but it's more complex because > it is CORRECT!
Since you emphasised on correctness, your code is actually buggy for the preemptible kernel. It could get preempted after the ready() test, but before the time_after(), for quite a whie if a high priority process keeps the system busy. This code is better:
unsigned long timeout = jiffies + HZ/2; int err; for (;;) { err = time_after(timeout, jiffies); if (ready()) return 0; if (err) break; msleep(10); }
This way the condition is always re-tested before reporting timeout.
Johannes - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |