From: Alexei Starovoitov <ast@fb•com>
To: Peter Zijlstra <peterz@infradead•org>
Cc: Steven Rostedt <rostedt@goodmis•org>,
"David S . Miller" <davem@davemloft•net>,
Ingo Molnar <mingo@kernel•org>,
Daniel Borkmann <daniel@iogearbox•net>,
Arnaldo Carvalho de Melo <acme@infradead•org>,
Wang Nan <wangnan0@huawei•com>, Josef Bacik <jbacik@fb•com>,
Brendan Gregg <brendan.d.gregg@gmail•com>,
<netdev@vger•kernel.org>, <linux-kernel@vger•kernel.org>,
<kernel-team@fb•com>
Subject: Re: [PATCH net-next 1/8] perf: optimize perf_fetch_caller_regs
Date: Tue, 5 Apr 2016 10:41:03 -0700 [thread overview]
Message-ID: <5703F8AF.7040503@fb.com> (raw)
In-Reply-To: <20160405120626.GM3448@twins.programming.kicks-ass.net>
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.
next prev parent reply other threads:[~2016-04-05 17:41 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-05 4:52 [PATCH net-next 0/8] allow bpf attach to tracepoints Alexei Starovoitov
2016-04-05 4:52 ` [PATCH net-next 1/8] perf: optimize perf_fetch_caller_regs Alexei Starovoitov
2016-04-05 12:06 ` Peter Zijlstra
2016-04-05 17:41 ` Alexei Starovoitov [this message]
2016-04-08 22:12 ` Steven Rostedt
2016-04-05 4:52 ` [PATCH net-next 2/8] perf, bpf: allow bpf programs attach to tracepoints Alexei Starovoitov
2016-04-05 14:18 ` Peter Zijlstra
2016-04-05 18:09 ` Alexei Starovoitov
2016-04-05 18:16 ` Peter Zijlstra
2016-04-05 18:21 ` Alexei Starovoitov
2016-04-18 20:29 ` Steven Rostedt
2016-04-18 21:43 ` Alexei Starovoitov
2016-04-18 22:16 ` Steven Rostedt
2016-04-19 1:15 ` Alexei Starovoitov
2016-04-19 2:58 ` Steven Rostedt
2016-04-05 4:52 ` [PATCH net-next 3/8] bpf: register BPF_PROG_TYPE_TRACEPOINT program type Alexei Starovoitov
2016-04-05 4:52 ` [PATCH net-next 4/8] bpf: support bpf_get_stackid() and bpf_perf_event_output() in tracepoint programs Alexei Starovoitov
2016-04-05 4:52 ` [PATCH net-next 5/8] bpf: sanitize bpf tracepoint access Alexei Starovoitov
2016-04-05 4:52 ` [PATCH net-next 6/8] samples/bpf: add tracepoint support to bpf loader Alexei Starovoitov
2016-04-05 4:52 ` [PATCH net-next 7/8] samples/bpf: tracepoint example Alexei Starovoitov
2016-04-05 4:52 ` [PATCH net-next 8/8] samples/bpf: add tracepoint vs kprobe performance tests Alexei Starovoitov
2016-04-18 16:13 ` [PATCH net-next 0/8] allow bpf attach to tracepoints Steven Rostedt
2016-04-18 19:51 ` Alexei Starovoitov
2016-04-18 20:47 ` Steven Rostedt
2016-04-18 21:25 ` Alexei Starovoitov
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