On Sat, Nov 11, 2017 at 01:59:21AM -0200, Marcelo Tosatti wrote: > On Fri, Nov 10, 2017 at 08:51:02AM -0500, Luiz Capitulino wrote: > > On Fri, 10 Nov 2017 11:14:51 +0000 > > Bruce Richardson <bruce.richard...@intel.com> wrote: > > > > > On Fri, Nov 10, 2017 at 11:42:56AM +0100, Daniel Bristot de Oliveira > > > wrote: > > > > > > > > > > > > On 11/10/2017 11:14 AM, Ananyev, Konstantin wrote: > > > > > Agree with Adrian here - the patch doesn't fix the problem in any > > > > > case, > > > > > > > > I would agree with you if it were possible to assume one can fully > > > > isolate a CPU on Linux... but it is not... > > > > > > > > This: > > > > https://lwn.net/Articles/659490/ > > > > > > > > is still an open issue, and the reason why it is an open issue is the > > > > kernel threads that need to run on every CPU, mainly when using the > > > > PREEMPT_RT, which turns almost everything on threads. > > > > > > > > > while introducing an unnecessary slowdown in testpmd iofwd mode. > > > > > Please think up some other approach. > > > > > > > > The other approach is to increase the priority of all other threads that > > > > run on the isolate CPU. But that is not a good idea at all, as the other > > > > threads might preempt the busy-loop thread at the worst possible moment. > > > > > > > > Using the knowledge of the thread about when it is the best time to give > > > > a chance for other threads to run would be a smarter decision. > > > > > > > I don't like having this in the main loop either, and to echo others I > > > wouldn't have thought that testpmd was actually used as anything other > > > than a testing app. > > > > That's why we're patching it. We want to be aware of the implications. > > If it's not good for testpmd, it may not be good for production either. > > The arguments raised so far against the patch have been: > > 1) Performance is reduced. > Reply: > * Of course performance is reduced, but any solution will also > reduce performance similary. > * Performance is reduced but within the acceptable limits set by > NFV standards. So the performance reduction argument is kind > of not an issue (in my POV). > > 2) Testpmd is a test application. > > Well, if one would like to avoid XFS corruption or other similar > results caused by the not possibility of running poll mode testpmd > (while testing) then he should enable the options (which are disabled > by default). Moreover, testpmd is an example application used by > production developers, so it should be integrated to testpmd. > > > Does anyone have arguments against the reasoning above ?
Note: yes the kernel seems to be the proper place to fix this, however: 1) It'll take some time to fix the kernel to handle the problem. 2) In the meantime, a temporary workaround in DPDK is available.
