From: Alexander Shishkin <alexander.shishkin@linux.intel.com>
To: Peter Zijlstra <peterz@infradead.org>,
mingo@kernel.org, peterz@infradead.org,
linux-kernel@vger.kernel.org
Cc: acme@kernel.org, mark.rutland@arm.com, jolsa@redhat.com,
namhyung@kernel.org, andi@firstfloor.org,
kan.liang@linux.intel.com, alexander.shishkin@linux.intel.com
Subject: Re: [PATCH 1/3] perf: Optimize perf_install_in_event()
Date: Wed, 23 Oct 2019 15:30:27 +0300 [thread overview]
Message-ID: <874kzz4pb0.fsf@ashishki-desk.ger.corp.intel.com> (raw)
In-Reply-To: <20191022092307.368892814@infradead.org>
Peter Zijlstra <peterz@infradead.org> writes:
> + /*
> + * perf_event_attr::disabled events will not run and can be initialized
> + * without IPI. Except when this is the first event for the context, in
> + * that case we need the magic of the IPI to set ctx->is_active.
> + *
> + * The IOC_ENABLE that is sure to follow the creation of a disabled
> + * event will issue the IPI and reprogram the hardware.
> + */
> + if (__perf_effective_state(event) == PERF_EVENT_STATE_OFF && ctx->nr_events) {
> + raw_spin_lock_irq(&ctx->lock);
> + if (task && ctx->task == TASK_TOMBSTONE) {
Confused: isn't that redundant? If ctx->task reads TASK_TOMBSTONE, task
is always !NULL, afaict. And in any case, if a task context is going
away, we shouldn't probably be adding events there. Or am I missing
something?
Other than that, this makes sense to me, fwiw.
Regards,
--
Alex
next prev parent reply other threads:[~2019-10-23 12:34 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-22 9:20 [PATCH 0/3] Various optimizations for event creation Peter Zijlstra
2019-10-22 9:20 ` [PATCH 1/3] perf: Optimize perf_install_in_event() Peter Zijlstra
2019-10-22 10:03 ` Peter Zijlstra
2019-10-23 12:30 ` Alexander Shishkin [this message]
2019-10-23 13:44 ` Peter Zijlstra
2019-10-23 14:08 ` Peter Zijlstra
2019-10-22 9:20 ` [PATCH 2/3] perf: Optimize perf_init_event() Peter Zijlstra
2019-10-27 5:18 ` [perf] 06e0dbcfd3: phoronix-test-suite.mbw.0.mib_s 12.6% improvement kernel test robot
2019-10-27 5:18 ` kernel test robot
2019-10-27 16:32 ` Andi Kleen
2019-10-22 9:20 ` [PATCH 3/3] perf: Optimize perf_init_event() for TYPE_SOFTWARE Peter Zijlstra
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