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    SubjectRe: [PATCH net-next 1/8] perf: optimize perf_fetch_caller_regs
    On Mon, Apr 04, 2016 at 09:52:47PM -0700, Alexei Starovoitov wrote:
    > avoid memset in perf_fetch_caller_regs, since it's the critical path of all tracepoints.
    > It's called from perf_sw_event_sched, perf_event_task_sched_in and all of perf_trace_##call
    > with this_cpu_ptr(&__perf_regs[..]) which are zero initialized by perpcu_alloc

    Its not actually allocated; but because its a static uninitialized
    variable we get .bss like behaviour and the initial value is copied to
    all CPUs when the per-cpu allocator thingy bootstraps SMP IIRC.

    > and
    > subsequent call to perf_arch_fetch_caller_regs initializes the same fields on all archs,
    > so we can safely drop memset from all of the above cases and

    Indeed.

    > move it into
    > perf_ftrace_function_call that calls it with stack allocated pt_regs.

    Hmm, is there a reason that's still on-stack instead of using the
    per-cpu thing, Steve?

    > Signed-off-by: Alexei Starovoitov <ast@kernel.org>

    In any case,

    Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>

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