Hello, Lai. On Tue, Sep 25, 2012 at 05:02:43PM +0800, Lai Jiangshan wrote: > It is not possible to remove cascading. If cascading code is > not in flush_workqueue(), it must be in some where else.
Yeah, sure, I liked that it didn't have to be done explicitly as a separate step. > If you force overflow to wait for freed color before do flush(which also > force only one flusher for one color), and force the sole flush_workqueue() > to grab ->flush_mutex twice, we can simplify the flush_workqueue(). > (see the attached patch, it remove 100 LOC, and the cascading code becomes > only 3 LOC). But these two forcing slow down the caller a little. Hmmm... so, that's a lot simpler. flush_workqueue() isn't a super-hot code path and I don't think grabbing mutex twice is too big a deal. I haven't actually reviewed the code but if it can be much simpler and thus easier to understand and verify, I might go for that. > (And if you allow to use SRCU(which is only TWO colors), you can remove > another > 150 LOC. flush_workqueue() will become single line. But it will add some more > overhead > in flush_workqueue() because SRCU's readsite is lockless) I'm not really following how SRCU would factor into this but supporting multiple colors was something explicitly requested by Linus. The initial implementation was a lot simpler which supported only two colors. Linus was worried that the high possibility of flusher clustering could lead to chaining of latencies. Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
