From: Peter Zijlstra <peterz@infradead•org>
To: Alexei Starovoitov <ast@plumgrid•com>
Cc: Kaixu Xia <xiakaixu@huawei•com>,
davem@davemloft•net, acme@kernel•org, mingo@redhat•com,
masami.hiramatsu.pt@hitachi•com, jolsa@kernel•org,
daniel@iogearbox•net, wangnan0@huawei•com,
linux-kernel@vger•kernel.org, pi3orama@163•com,
hekuang@huawei•com, netdev@vger•kernel.org
Subject: Re: [PATCH v6 3/4] bpf: Implement function bpf_perf_event_read() that get the selected hardware PMU conuter
Date: Wed, 5 Aug 2015 18:21:52 +0200 [thread overview]
Message-ID: <20150805162152.GC25159@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <55C23500.1000207@plumgrid.com>
On Wed, Aug 05, 2015 at 09:08:32AM -0700, Alexei Starovoitov wrote:
> On 8/5/15 6:53 AM, Peter Zijlstra wrote:
> >+ /*
> >+ * If the event is currently on this CPU, its either a per-task event,
> >+ * or local to this CPU. Furthermore it means its ACTIVE (otherwise
> >+ * oncpu == -1).
> >+ */
> >+ if (event->oncpu == smp_processor_id())
> >+ event->pmu->read(event);
> >+
> >+ val = local64_read(&event->count);
> >+ local_irq_restore(flags);
> >+
>
> nice! cleaner and faster.
> so raw_spin_lock(&ctx->lock) is not needed, because
> update_*(event) methods are not called, right?
Indeed, and by ensuring the event is indeed local (by force of WARN_ON)
disabling IRQs will avoid counter scheduling and result in a stable
event state.
next prev parent reply other threads:[~2015-08-05 16:21 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-08-04 8:58 [PATCH v6 0/4] bpf: Introduce the new ability of eBPF programs to access hardware PMU counter Kaixu Xia
2015-08-04 8:58 ` [PATCH v6 1/4] bpf: Make the bpf_prog_array_map more generic Kaixu Xia
2015-08-04 8:58 ` [PATCH v6 2/4] bpf: Add new bpf map type to store the pointer to struct perf_event Kaixu Xia
2015-08-04 17:43 ` Alexei Starovoitov
2015-08-05 9:41 ` Peter Zijlstra
2015-08-05 9:39 ` Peter Zijlstra
2015-08-05 9:43 ` Peter Zijlstra
2015-08-04 8:58 ` [PATCH v6 3/4] bpf: Implement function bpf_perf_event_read() that get the selected hardware PMU conuter Kaixu Xia
2015-08-04 17:55 ` Alexei Starovoitov
2015-08-05 2:09 ` xiakaixu
2015-08-05 10:04 ` Peter Zijlstra
2015-08-05 10:15 ` Peter Zijlstra
2015-08-05 16:00 ` Alexei Starovoitov
2015-08-05 10:31 ` xiakaixu
2015-08-05 13:53 ` Peter Zijlstra
2015-08-05 13:59 ` Peter Zijlstra
2015-08-05 16:08 ` Alexei Starovoitov
2015-08-05 16:21 ` Peter Zijlstra [this message]
2015-08-06 2:49 ` xiakaixu
2015-08-05 15:59 ` Alexei Starovoitov
2015-08-04 8:58 ` [PATCH v6 4/4] samples/bpf: example of get selected PMU counter value Kaixu Xia
2015-08-05 10:06 ` [PATCH v6 0/4] bpf: Introduce the new ability of eBPF programs to access hardware PMU counter Peter Zijlstra
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