Re: [PATCH] perf, x86: Disable sanity check

From: Arun Sharma
Date: Fri Apr 20 2012 - 14:19:56 EST

On 4/20/12 2:11 AM, Peter Zijlstra wrote:
Makes me really nervous.. Ingo, Linus ?

'normal' usespace can suffer from this too with signal stacks. Arun's
JIT case seems particularly weird in that his stacks don't strictly nest
but can cross over multiple times (makes one wonder why they bother with
multiple stacks..).

It's a tracing JIT, which dynamically chooses between interpreted mode and JIT mode. Translation is not necessarily a function at a time and has to be guarded by types inferred at runtime. Each time they switch between the two modes, they need to examine the non-native frames on the stack. With a single stack design, they'd have to unwind the stack looking for native frames vs JIT frames which adds complexity and cost.

Like you observed, this is needed for other less complex cases as well.


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