Messages in this thread | | | Date | Sat, 21 Feb 2015 17:08:52 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH tip/core/rcu 0/4] Programmatic nestable expedited grace periods |
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On Fri, Feb 20, 2015 at 09:45:39AM -0800, Arjan van de Ven wrote: > On 2/20/2015 9:43 AM, Peter Zijlstra wrote: > >On Fri, Feb 20, 2015 at 09:32:39AM -0800, Arjan van de Ven wrote: > >>there's a few others as well that I'm chasing down... > >>.. but the flip side, prior to running ring 3 code, why NOT do fast expedites? > > > >So my objections are twofold: > > > > - I object to fast expedites in principle; they spray IPIs across the > > system, so ideally we'd not have them at all, therefore also not at > > boot. > > > > Because as soon as the option exists, people will use it for other > > things too. > > the option exists today in sysfs and kernel parameter...
Yeah, Paul and me have been having this argument for a while now ;-)
> >And esp. in bootup code you can special case a lot of stuff; there's > >limited concurrency esp. because userspace it not there yet. So we might > >not actually need those sync calls. > > yeah I am going down that angle as well absolutely. > but there are cases that may well be legit (or are 5 function calls deep into common code)
Good ;-)
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