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From: Thomas Gleixner <tglx@linutronix.de>
To: Nitesh Lal <nilal@redhat.com>,
	Jesse Brandeburg <jesse.brandeburg@intel.com>,
	Robin Murphy <robin.murphy@arm.com>,
	Marcelo Tosatti <mtosatti@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>,
	linux-kernel@vger.kernel.org, intel-wired-lan@lists.osuosl.org,
	jbrandeb@kernel.org, "frederic\@kernel.org" <frederic@kernel.org>,
	"juri.lelli\@redhat.com" <juri.lelli@redhat.com>,
	Alex Belits <abelits@marvell.com>,
	"linux-api\@vger.kernel.org" <linux-api@vger.kernel.org>,
	"bhelgaas\@google.com" <bhelgaas@google.com>,
	"linux-pci\@vger.kernel.org" <linux-pci@vger.kernel.org>,
	"rostedt\@goodmis.org" <rostedt@goodmis.org>,
	"peterz\@infradead.org" <peterz@infradead.org>,
	"davem\@davemloft.net" <davem@davemloft.net>,
	"akpm\@linux-foundation.org" <akpm@linux-foundation.org>,
	"sfr\@canb.auug.org.au" <sfr@canb.auug.org.au>,
	"stephen\@networkplumber.org" <stephen@networkplumber.org>,
	"rppt\@linux.vnet.ibm.com" <rppt@linux.vnet.ibm.com>,
	"jinyuqi\@huawei.com" <jinyuqi@huawei.com>,
	"zhangshaokun\@hisilicon.com" <zhangshaokun@hisilicon.com>,
	netdev@vger.kernel.org, chris.friesen@windriver.com,
	Marc Zyngier <maz@kernel.org>,
	Neil Horman <nhorman@tuxdriver.com>,
	pjwaskiewicz@gmail.com
Subject: [PATCH] genirq: Provide new interfaces for affinity hints
Date: Fri, 21 May 2021 14:03:06 +0200	[thread overview]
Message-ID: <87wnrs9tvp.ffs@nanos.tec.linutronix.de> (raw)
In-Reply-To: <87zgwo9u79.ffs@nanos.tec.linutronix.de>

The discussion about removing the side effect of irq_set_affinity_hint() of
actually applying the cpumask (if not NULL) as affinity to the interrupt,
unearthed a few unpleasantries:

  1) The modular perf drivers rely on the current behaviour for the very
     wrong reasons.

  2) While none of the other drivers prevents user space from changing
     the affinity, a cursorily inspection shows that there are at least
     expectations in some drivers.

#1 needs to be cleaned up anyway, so that's not a problem

#2 might result in subtle regressions especially when irqbalanced (which
   nowadays ignores the affinity hint) is disabled.

Provide new interfaces:

  irq_update_affinity_hint() - Only sets the affinity hint pointer
  irq_apply_affinity_hint()  - Set the pointer and apply the affinity to
  			       the interrupt

Make irq_set_affinity_hint() a wrapper around irq_apply_affinity_hint() and
document it to be phased out.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20210501021832.743094-1-jesse.brandeburg@intel.com
---
Applies on:
   git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git irq/core
---
 include/linux/interrupt.h |   41 ++++++++++++++++++++++++++++++++++++++++-
 kernel/irq/manage.c       |    8 ++++----
 2 files changed, 44 insertions(+), 5 deletions(-)

--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -328,7 +328,46 @@ extern int irq_force_affinity(unsigned i
 extern int irq_can_set_affinity(unsigned int irq);
 extern int irq_select_affinity(unsigned int irq);
 
-extern int irq_set_affinity_hint(unsigned int irq, const struct cpumask *m);
+extern int __irq_apply_affinity_hint(unsigned int irq, const struct cpumask *m,
+				     bool setaffinity);
+
+/**
+ * irq_update_affinity_hint - Update the affinity hint
+ * @irq:	Interrupt to update
+ * @cpumask:	cpumask pointer (NULL to clear the hint)
+ *
+ * Updates the affinity hint, but does not change the affinity of the interrupt.
+ */
+static inline int
+irq_update_affinity_hint(unsigned int irq, const struct cpumask *m)
+{
+	return __irq_apply_affinity_hint(irq, m, true);
+}
+
+/**
+ * irq_apply_affinity_hint - Update the affinity hint and apply the provided
+ *			     cpumask to the interrupt
+ * @irq:	Interrupt to update
+ * @cpumask:	cpumask pointer (NULL to clear the hint)
+ *
+ * Updates the affinity hint and if @cpumask is not NULL it applies it as
+ * the affinity of that interrupt.
+ */
+static inline int
+irq_apply_affinity_hint(unsigned int irq, const struct cpumask *m)
+{
+	return __irq_apply_affinity_hint(irq, m, true);
+}
+
+/*
+ * Deprecated. Use irq_update_affinity_hint() or irq_apply_affinity_hint()
+ * instead.
+ */
+static inline int irq_set_affinity_hint(unsigned int irq, const struct cpumask *m)
+{
+	return irq_apply_affinity_hint(irq, cpumask);
+}
+
 extern int irq_update_affinity_desc(unsigned int irq,
 				    struct irq_affinity_desc *affinity);
 
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -487,7 +487,8 @@ int irq_force_affinity(unsigned int irq,
 }
 EXPORT_SYMBOL_GPL(irq_force_affinity);
 
-int irq_set_affinity_hint(unsigned int irq, const struct cpumask *m)
+int __irq_apply_affinity_hint(unsigned int irq, const struct cpumask *m,
+			      bool setaffinity)
 {
 	unsigned long flags;
 	struct irq_desc *desc = irq_get_desc_lock(irq, &flags, IRQ_GET_DESC_CHECK_GLOBAL);
@@ -496,12 +497,11 @@ int irq_set_affinity_hint(unsigned int i
 		return -EINVAL;
 	desc->affinity_hint = m;
 	irq_put_desc_unlock(desc, flags);
-	/* set the initial affinity to prevent every interrupt being on CPU0 */
-	if (m)
+	if (m && setaffinity)
 		__irq_set_affinity(irq, m, false);
 	return 0;
 }
-EXPORT_SYMBOL_GPL(irq_set_affinity_hint);
+EXPORT_SYMBOL_GPL(__irq_apply_affinity_hint);
 
 static void irq_affinity_notify(struct work_struct *work)
 {

  reply	other threads:[~2021-05-21 12:03 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-01  2:18 [PATCH tip:irq/core v1] genirq: remove auto-set of the mask when setting the hint Jesse Brandeburg
2021-05-04 12:15 ` Robin Murphy
2021-05-04 14:29   ` Nitesh Lal
2021-05-04 16:23   ` Jesse Brandeburg
2021-05-17 16:57     ` Nitesh Lal
2021-05-17 17:26       ` Robin Murphy
2021-05-17 18:08         ` Thomas Gleixner
2021-05-17 18:50           ` Robin Murphy
2021-05-17 19:08             ` Thomas Gleixner
2021-05-17 19:43               ` Thomas Gleixner
2021-05-17 20:18               ` Thomas Gleixner
2021-05-17 18:21         ` Nitesh Lal
2021-05-17 19:47           ` Thomas Gleixner
2021-05-17 21:13             ` Nitesh Lal
2021-05-17 20:48     ` Thomas Gleixner
2021-05-17 22:44       ` Nitesh Lal
2021-05-18  0:03         ` Thomas Gleixner
2021-05-18  0:23           ` Nitesh Lal
2021-05-20 21:57             ` Nitesh Lal
2021-05-21  0:03               ` Nitesh Lal
2021-05-21 11:56                 ` Thomas Gleixner
2021-05-21 12:03                   ` Thomas Gleixner [this message]
2021-05-21 15:45                     ` [PATCH] genirq: Provide new interfaces for affinity hints Lijun Pan
2021-05-21 21:45                       ` Thomas Gleixner
2021-05-21 16:13                     ` Nitesh Lal
2021-05-21 21:48                       ` Thomas Gleixner
2021-06-04 20:35                         ` Nitesh Lal
2021-05-27 10:03                     ` Shung-Hsi Yu
2021-05-27 10:21                       ` Shung-Hsi Yu
2021-05-27 13:06                       ` Nitesh Lal
2021-05-28  7:20                         ` Shung-Hsi Yu
2021-06-07 17:00                     ` Nitesh Lal
2021-06-14 16:12                       ` Nitesh Lal
2021-05-21 13:46                   ` [PATCH tip:irq/core v1] genirq: remove auto-set of the mask when setting the hint Nitesh Lal
2021-05-21 15:15                     ` Thomas Gleixner
2021-12-10 19:54 ` [tip: irq/core] genirq: Provide new interfaces for affinity hints tip-bot2 for Thomas Gleixner

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