Re: [PATCH] genirq: Provide new interfaces for affinity hints
From: Shung-Hsi Yu <hidden>
Date: 2021-05-27 10:03:53
Also in:
intel-wired-lan, linux-api, linux-pci, lkml
Hi, On Fri, May 21, 2021 at 02:03:06PM +0200, Thomas Gleixner wrote:
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.
Is there recommended way to retrieve the CPU number that the interrupt has
affinity?
Previously a driver (I'm looking at drivers/net/ethernet/amazon/ena) that
uses irq_set_affinity_hint() to spread out IRQ knows the corresponding CPU
number since they're using their own spreading scheme. Now, phasing out
irq_set_affinity_hint(), and thus relying on request_irq() to spread the
load instead, there don't seem to be a easy way to get the CPU number.
In theory the following could work, but including irq.h does not look like a
good idea given that the comment in its explicitly ask not to be included in
generic code.
#include <linux/irq.h>
int irq = request_irq(...);
struct irq_data *data = irq_get_irq_data(irq);
struct cpumask *mask = irq_data_get_effective_affinity_mask(data);
int cpu = cpumask_first(mask);
Any suggestions?
Thanks,
Shung-Hsi
quoted hunk ↗ jump to hunk
Signed-off-by: Thomas Gleixner <redacted> Link: https://lore.kernel.org/r/20210501021832.743094-1-jesse.brandeburg@intel.com (local) --- 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) {