Messages in this thread | | | Date | Fri, 5 Apr 2019 23:56:29 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: [patch V2 20/29] x86/dumpstack/64: Speedup in_exception_stack() |
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On Fri, 5 Apr 2019, Josh Poimboeuf wrote: > On Fri, Apr 05, 2019 at 05:07:18PM +0200, Thomas Gleixner wrote: > > The current implementation of in_exception_stack() iterates over the > > exception stacks array. Most of the time this is an useless exercise, but > > even for the actual use cases (perf and ftrace) it takes at least 2 > > iterations to get to the NMI stack. > > > > As the exception stacks and the guard pages are page aligned the loop can > > be avoided completely. > > > > Add a initial check whether the stack pointer is inside the full exception > > stack area and leave early if not. > > > > Create a lookup table which describes the stack area. The table index is > > the page offset from the beginning of the exception stacks. So for any > > given stack pointer the page offset is computed and a lookup in the > > description table is performed. If it is inside a guard page, return. If > > not, use the descriptor to fill in the info structure. > > > > The table is filled at compile time and for the !KASAN case the interesting > > page descriptors exactly fit into a single cache line. Just the last guard > > page descriptor is in the next cacheline, but that should not be accessed > > in the regular case. > > > > Signed-off-by: Thomas Gleixner <tglx@linutronix.de> > > --- > > V2: Simplify the macro maze > > This is indeed a little better. It's friday, have an ack. > > Acked-by: Josh Poimboeuf <jpoimboe@redhat.com> > > I don't like the clever ISTACK_* macro naming however...
Come on it's friday, time for a little bikeshedding :)
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