Messages in this thread | | | Date | Fri, 15 Sep 2017 12:15:38 -0700 | From | Stephen Boyd <> | Subject | Re: [PATCH] arm64: Unconditionally support ARCH_HAVE_NMI_SAFE_CMPXCHG |
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On 09/15, James Morse wrote: > On 15/09/17 02:19, Stephen Boyd wrote: > > From what I can see there isn't anything about ACPI_APEI_SEA that > > means the arm64 architecture can or cannot support NMI safe > > cmpxchg, so the if condition here is not important. > > Yup, it was to match 'HAVE_NMI', which was new with ACPI_APEI_SEA and pulls in > some printk() stuff. > > ... how come you don't need to change HAVE_NMI too?
I didn't change HAVE_NMI because it wasn't needed to get hist triggers working. Sorry, I didn't even notice that HAVE_NMI was also there, probably both of these configs should drop the condition. I'll update the patch to do so.
> > > > Let's remove > > it. Doing that allows us to support ftrace histograms via > > CONFIG_HIST_TRIGGERS that depends on the arch having this config > > selected. > > What does CONFIG_HIST_TRIGGERS need this for? I can't see any > cmpxchg use in kernel/trace/trace_events_hist.c
True. I think this isn't necessary for CONFIG_HIST_TRIGGERS, but more for CONFIG_TRACING_MAP that is selected and used by CONFIG_HIST_TRIGGERS. We put the dependency in both places so we don't get the trigger config selecting a config that has unmet dependencies. Note there's a cmpxchg in the tracing map code too.
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