Messages in this thread | | | Date | Sat, 21 Feb 2015 19:58:07 -0800 | From | Josh Triplett <> | Subject | Re: [PATCH tip/core/rcu 0/4] Programmatic nestable expedited grace periods |
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On Sat, Feb 21, 2015 at 07:51:34AM -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? > > > >It would be good to have before-and-after measurements of actual > >boot time. Are these numbers available? > > To show the boot time, I'm using the timestamp of the "Write protecting" line, > that's pretty much the last thing we print prior to ring 3 execution.
That's a little sad; we ought to be write-protecting kernel read-only data as *early* as possible.
> A kernel with default RCU behavior (inside KVM, only virtual devices) looks like this: > > [ 0.038724] Write protecting the kernel read-only data: 10240k > > a kernel with expedited RCU (using the command line option, so that I don't have > to recompile between measurements and thus am completely oranges-to-oranges) > > [ 0.031768] Write protecting the kernel read-only data: 10240k > > which, in percentage, is an 18% improvement.
Nice improvement, but that suggests that we're spending far too much time waiting on RCU grace periods at boot time.
- Josh Triplett
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