Messages in this thread | | | Subject | Re: [PATCH net-next 1/8] perf: optimize perf_fetch_caller_regs | From | Alexei Starovoitov <> | Date | Tue, 5 Apr 2016 10:41:03 -0700 |
| |
On 4/5/16 5:06 AM, Peter Zijlstra wrote: > 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.
yes, it's .bss-like in a special section. I think static percpu still goes through some fancy boot time init similar to dynamic. What I tried to emphasize that either static or dynamic percpu areas are guaranteed to be zero initialized.
>> 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>
Thanks for the quick review.
| |