On 03/09/2014 10:51, Michael S. Tsirkin wrote: > On Wed, Sep 03, 2014 at 09:49:10AM +0300, Eliezer Tamir wrote: >> On 02/09/2014 11:31, Michael S. Tsirkin wrote: >>> On Tue, Sep 02, 2014 at 09:15:18AM +0300, Eliezer Tamir wrote:
>> Busy polling is not a general purpose feature, it's not something you >> can casually turn on and will "just work". Most applications should not >> be using busy polling. Currently it is used by multiserver applications >> that you spend days tuning to specific platforms. >> >> What the user wants is to lower both avg and maximum latencies, at the >> expense of everything else including power efficiency and sometimes >> even throughput. The only exception is making the system crash ;) >> >> While letting other things take precedence over busy polling might not >> hurt the avg latency much, it will kill your maximum latency. > > If scheduler happens to run both server and client on the > same CPU, polling will hurt maximum latency even more. > So I guess different users want different things. > > How about applications giving us a hint what they prefer? > For example, a new flag that says "I don't have anything useful to do so > let's do busy polling but my server is on the local system, so please > only poll if CPU is otherwise idle". I'm sorry for being ambiguous, when I said multi-server application, I meant an app that runs on more than one server machine. The loopback test is as far as I know not interesting. Of course if busypoll becomes interesting for virtualization over loopback, I have no problem with that, provided that there is a way to get the old behavior and that it is well documented. -Eliezer -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
