Messages in this thread |  | | | Subject | Re: [PATCH 1/5] ftrace: Synchronize variable setting with breakpoints | | From | Steven Rostedt <> | | Date | Thu, 31 May 2012 16:49:20 -0400 |
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On Thu, 2012-05-31 at 22:40 +0200, Peter Zijlstra wrote: > On Thu, 2012-05-31 at 16:37 -0400, Steven Rostedt wrote: > > On Thu, 2012-05-31 at 22:26 +0200, Peter Zijlstra wrote: > > > > > Right, but when you loose stop-machine you could simply do 30k > > > kmap_atomic/kunmap_atomic's consecutively since you're not holding > > > anybody up. > > > > It requires 3 IPIs per update too. Thus that's 90,000 IPIs you are > > blasting^Wsending to all CPUs. > > Uhm, no. >
----------------------------------+ > for_each() { | > kmap_atomic() | > frob int3 | > kunmap_atomic(); | > } | > | > sync-ipi-broadcast(); +--- Break points applied > | > for_each() { | > kmap_atomic(); | > frob tail | > kunmap_atomic(); | > } | ----------------------------------+ Note, for the above time, the entire kernel has breakpoints added, and every function is taking a hit due to it. By slowing down this process, the rest of the system *will* be impacted. Ideally, we want to finish it as quick as possible. Not to mention, the kmap_atomics will be slowed down by the breakpoints that are attached to them.
-- Steve
> > sync-ipi-broadcast(); > > for_each() { > kmap_atomic(); > frob head > kunmap_atomic(); > }; > > sync-ipi-broadcast(); > > How is that sending 90k ipis?
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