From: Peter Zijlstra <peterz@infradead.org>
To: Valentin Schneider <vschneid@redhat.com>
Cc: linux-alpha@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-snps-arc@lists.infradead.org,
linux-arm-kernel@lists.infradead.org, linux-csky@vger.kernel.org,
linux-hexagon@vger.kernel.org, linux-ia64@vger.kernel.org,
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linux-s390@vger.kernel.org, linux-sh@vger.kernel.org,
sparclinux@vger.kernel.org, linux-xtensa@linux-xtensa.org,
x86@kernel.org, "Paul E. McKenney" <paulmck@kernel.org>,
Steven Rostedt <rostedt@goodmis.org>,
Thomas Gleixner <tglx@linutronix.de>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
Juri Lelli <juri.lelli@redhat.com>,
Daniel Bristot de Oliveira <bristot@redhat.com>,
Marcelo Tosatti <mtosatti@redhat.com>,
Frederic Weisbecker <frederic@kernel.org>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
"H. Peter Anvin" <hpa@zytor.com>, Marc Zyngier <maz@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Russell King <linux@armlinux.org.uk>,
Nicholas Piggin <npiggin@gmail.com>, Guo Ren <guoren@kernel.org>,
"David S. Miller" <davem@davemloft.net>
Subject: Re: [PATCH v5 7/7] sched, smp: Trace smp callback causing an IPI
Date: Wed, 22 Mar 2023 10:53:29 +0100 [thread overview]
Message-ID: <20230322095329.GS2017917@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20230307143558.294354-8-vschneid@redhat.com>
On Tue, Mar 07, 2023 at 02:35:58PM +0000, Valentin Schneider wrote:
> @@ -477,6 +490,25 @@ static __always_inline void csd_unlock(struct __call_single_data *csd)
> smp_store_release(&csd->node.u_flags, 0);
> }
>
> +static __always_inline void
> +raw_smp_call_single_queue(int cpu, struct llist_node *node, smp_call_func_t func)
> +{
> + /*
> + * The list addition should be visible to the target CPU when it pops
> + * the head of the list to pull the entry off it in the IPI handler
> + * because of normal cache coherency rules implied by the underlying
> + * llist ops.
> + *
> + * If IPIs can go out of order to the cache coherency protocol
> + * in an architecture, sufficient synchronisation should be added
> + * to arch code to make it appear to obey cache coherency WRT
> + * locking and barrier primitives. Generic code isn't really
> + * equipped to do the right thing...
> + */
> + if (llist_add(node, &per_cpu(call_single_queue, cpu)))
> + send_call_function_single_ipi(cpu, func);
> +}
> +
> static DEFINE_PER_CPU_SHARED_ALIGNED(call_single_data_t, csd_data);
>
> void __smp_call_single_queue(int cpu, struct llist_node *node)
> @@ -493,21 +525,25 @@ void __smp_call_single_queue(int cpu, struct llist_node *node)
> }
> }
> #endif
> /*
> + * We have to check the type of the CSD before queueing it, because
> + * once queued it can have its flags cleared by
> + * flush_smp_call_function_queue()
> + * even if we haven't sent the smp_call IPI yet (e.g. the stopper
> + * executes migration_cpu_stop() on the remote CPU).
> */
> + if (trace_ipi_send_cpumask_enabled()) {
> + call_single_data_t *csd;
> + smp_call_func_t func;
> +
> + csd = container_of(node, call_single_data_t, node.llist);
> + func = CSD_TYPE(csd) == CSD_TYPE_TTWU ?
> + sched_ttwu_pending : csd->func;
> +
> + raw_smp_call_single_queue(cpu, node, func);
> + } else {
> + raw_smp_call_single_queue(cpu, node, NULL);
> + }
> }
Hurmph... so we only really consume @func when we IPI. Would it not be
more useful to trace this thing for *every* csd enqeued?
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next prev parent reply other threads:[~2023-03-22 9:53 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-07 14:35 [PATCH v5 0/7] Generic IPI sending tracepoint Valentin Schneider
2023-03-07 14:35 ` [PATCH v5 1/7] trace: Add trace_ipi_send_cpumask() Valentin Schneider
2023-03-22 9:39 ` Peter Zijlstra
2023-03-22 10:30 ` Peter Zijlstra
2023-03-22 11:24 ` Valentin Schneider
2023-03-07 14:35 ` [PATCH v5 2/7] sched, smp: Trace IPIs sent via send_call_function_single_ipi() Valentin Schneider
2023-03-07 14:35 ` [PATCH v5 3/7] smp: Trace IPIs sent via arch_send_call_function_ipi_mask() Valentin Schneider
2023-03-07 14:35 ` [PATCH v5 4/7] irq_work: Trace self-IPIs sent via arch_irq_work_raise() Valentin Schneider
2023-03-07 14:35 ` [PATCH v5 5/7] treewide: Trace IPIs sent via smp_send_reschedule() Valentin Schneider
2023-03-07 14:35 ` [PATCH v5 6/7] smp: reword smp call IPI comment Valentin Schneider
2023-03-07 14:35 ` [PATCH v5 7/7] sched, smp: Trace smp callback causing an IPI Valentin Schneider
2023-03-22 9:53 ` Peter Zijlstra [this message]
2023-03-22 12:20 ` Valentin Schneider
2023-03-22 14:04 ` Peter Zijlstra
2023-03-22 17:01 ` Valentin Schneider
2023-03-22 17:22 ` Peter Zijlstra
2023-03-22 18:22 ` Valentin Schneider
2023-03-22 23:14 ` Peter Zijlstra
2023-03-23 16:25 ` Valentin Schneider
2023-03-23 17:41 ` Peter Zijlstra
2023-03-23 18:31 ` Valentin Schneider
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