From: Nitesh Lal <nilal@redhat.com>
To: Shung-Hsi Yu <shung-hsi.yu@suse.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Jesse Brandeburg <jesse.brandeburg@intel.com>,
Robin Murphy <robin.murphy@arm.com>,
Marcelo Tosatti <mtosatti@redhat.com>,
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: Re: [PATCH] genirq: Provide new interfaces for affinity hints
Date: Thu, 27 May 2021 09:06:04 -0400 [thread overview]
Message-ID: <CAFki+LnuharcwJy=x4Z27ixCMK1u2s2cvHh9=Bcf90rO06osEw@mail.gmail.com> (raw)
In-Reply-To: <YK9ucRrjq+eck/G7@syu-laptop>
On Thu, May 27, 2021 at 6:03 AM Shung-Hsi Yu <shung-hsi.yu@suse.com> wrote:
>
> 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.
>
For drivers that don't want to rely on request_irq for spreading and want
to force their own affinity mask can use irq_set_affinity() which is an
exported interface now [1] and clearly indicates the purpose of the usage.
As Thomas suggested we are still keeping irq_set_affinity_hint() as a
wrapper until we make appropriate changes in individual drivers that use
this API for different reasons. Please feel free to send out a patch
for this driver once the changes are merged.
[1] https://lkml.org/lkml/2021/5/18/271
--
Thanks
Nitesh
next prev parent reply other threads:[~2021-05-27 13:06 UTC|newest]
Thread overview: 35+ 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 ` [PATCH] genirq: Provide new interfaces for affinity hints Thomas Gleixner
2021-05-21 15:45 ` 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 [this message]
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
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