Messages in this thread | | | Date | Sat, 5 Aug 2006 11:40:52 +0000 | From | Pavel Machek <> | Subject | Re: [patch] fix common mistake in polling loops |
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Hi!
> task taken from http://kerneljanitors.org/TODO: > > A _lot_ of drivers end up caring about absolute time, > because a _lot_ of > drivers have a very simple issue like: > > - poll this port every 10ms until it returns "ready", or > until we time > out after 500ms. > > And the thing is, you can do it the stupid way: > > for (i = 0; i < 50; i++) { > if (ready()) > return 0; > msleep(10); > } > .. timeout .. > > or you can do it the _right_ way. The stupid way is > simpler, but anybody > who doesn't see what the problem is has some serious > problems in kernel > programming. Hint: it might not be polling for half a
Well, whoever wrote thi has some serious problems (in attitude department). *Any* loop you design may take half a minute under streange circumstances.
> second, it might be > polling for half a _minute_ for all you know. > > In other words, the _right_ way to do this is literally > > unsigned long timeout = jiffies + > msecs_to_jiffies(500); > 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!
Original code is correct, too.
Anyway you probably want to hide complexity in some macro if we are going this way. Pavel -- Thanks for all the (sleeping) penguins. - 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/
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