Messages in this thread | | | Date | Tue, 19 May 2015 11:20:23 -0500 (CDT) | From | Christoph Lameter <> | Subject | Re: [GIT PULL] ring-buffer: Replace this_cpu_*() with __this_cpu_*() |
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On Tue, 19 May 2015, Steven Rostedt wrote:
> On Tue, 19 May 2015 10:35:32 -0500 (CDT) > Christoph Lameter <cl@linux.com> wrote: > > > On Thu, 19 Mar 2015, Steven Rostedt wrote: > > > > > On Thu, 19 Mar 2015 15:16:25 -0700 > > > Linus Torvalds <torvalds@linux-foundation.org> wrote: > > > > > > > So I don't think the ring-buffer change is necessarily _wrong_, but if > > > > this is a performance issue, why don't we just fix it up for the > > > > generic case rather than for just one user? > > > > > > I totally agree with your analysis, but it's up to Christoph to come up > > > with an answer to your questions. > > > > Something beyond: Do not use this_cpu_* when preemption is already > > off but use __this_cpu_*? > > I think the question was, why exactly does the generic this_cpu_read() > require disabling preemption? What breaks if it is not disabled?
Ok I answered that before. There is a cache line population/eviction issue (because it may happen on the wrong cache) but basically I think its mostly there for symmetries sake. We could remove this_cpu_read/write and let __this_cpu_read()/__this_cpu_write be used in non preemptible contexts.
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