From: Thomas Gleixner <tglx@linutronix.de> To: Nitesh Lal <nilal@redhat.com> Cc: Jesse Brandeburg <jesse.brandeburg@intel.com>, Robin Murphy <robin.murphy@arm.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>, Marcelo Tosatti <mtosatti@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> Subject: Re: [PATCH tip:irq/core v1] genirq: remove auto-set of the mask when setting the hint Date: Tue, 18 May 2021 02:03:57 +0200 [thread overview] Message-ID: <87im3gewlu.ffs@nanos.tec.linutronix.de> (raw) In-Reply-To: <CAFki+Lkjn2VCBcLSAfQZ2PEkx-TR0Ts_jPnK9b-5ne3PUX37TQ@mail.gmail.com> On Mon, May 17 2021 at 18:44, Nitesh Lal wrote: > On Mon, May 17, 2021 at 4:48 PM Thomas Gleixner <tglx@linutronix.de> wrote: >> The hint was added so that userspace has a better understanding where it >> should place the interrupt. So if irqbalanced ignores it anyway, then >> what's the point of the hint? IOW, why is it still used drivers? >> > Took a quick look at the irqbalance repo and saw the following commit: > > dcc411e7bf remove affinity_hint infrastructure > > The commit message mentions that "PJ is redesiging how affinity hinting > works in the kernel, the future model will just tell us to ignore an IRQ, > and the kernel will handle placement for us. As such we can remove the > affinity_hint recognition entirely". No idea who PJ is. I really love useful commit messages. Maybe Neil can shed some light on that. > This does indicate that apparently, irqbalance moved away from the usage of > affinity_hint. However, the next question is what was this future > model? I might have missed something in the last 5 years, but that's the first time I hear about someone trying to cleanup that thing. > I don't know but I can surely look into it if that helps or maybe someone > here already knows about it? I CC'ed Neil :) >> Now there is another aspect to that. What happens if irqbalanced does >> not run at all and a driver relies on the side effect of the hint >> setting the initial affinity. Bah... >> > > Right, but if they only rely on this API so that the IRQs are spread across > all the CPUs then that issue is already resolved and these other drivers > should not regress because of changing this behavior. Isn't it? Is that true for all architectures? >> While none of the drivers (except the perf muck) actually prevents >> userspace from fiddling with the affinity (via IRQF_NOBALANCING) a >> deeper inspection shows that they actually might rely on the current >> behaviour if irqbalanced is disabled. Of course every driver has its own >> convoluted way to do that and all of those functions are well >> documented. What a mess. >> >> If the hint still serves a purpose then we can provide a variant which >> solely applies the hint and does not fiddle with the actual affinity, >> but if the hint is useless anyway then we have a way better option to >> clean that up. >> > > +1 = 1 Thanks, tglx
WARNING: multiple messages have this Message-ID (diff)
From: Thomas Gleixner <tglx@linutronix.de> To: intel-wired-lan@osuosl.org Subject: [Intel-wired-lan] [PATCH tip:irq/core v1] genirq: remove auto-set of the mask when setting the hint Date: Tue, 18 May 2021 02:03:57 +0200 [thread overview] Message-ID: <87im3gewlu.ffs@nanos.tec.linutronix.de> (raw) In-Reply-To: <CAFki+Lkjn2VCBcLSAfQZ2PEkx-TR0Ts_jPnK9b-5ne3PUX37TQ@mail.gmail.com> On Mon, May 17 2021 at 18:44, Nitesh Lal wrote: > On Mon, May 17, 2021 at 4:48 PM Thomas Gleixner <tglx@linutronix.de> wrote: >> The hint was added so that userspace has a better understanding where it >> should place the interrupt. So if irqbalanced ignores it anyway, then >> what's the point of the hint? IOW, why is it still used drivers? >> > Took a quick look at the irqbalance repo and saw the following commit: > > dcc411e7bf remove affinity_hint infrastructure > > The commit message mentions that "PJ is redesiging how affinity hinting > works in the kernel, the future model will just tell us to ignore an IRQ, > and the kernel will handle placement for us. As such we can remove the > affinity_hint recognition entirely". No idea who PJ is. I really love useful commit messages. Maybe Neil can shed some light on that. > This does indicate that apparently, irqbalance moved away from the usage of > affinity_hint. However, the next question is what was this future > model? I might have missed something in the last 5 years, but that's the first time I hear about someone trying to cleanup that thing. > I don't know but I can surely look into it if that helps or maybe someone > here already knows about it? I CC'ed Neil :) >> Now there is another aspect to that. What happens if irqbalanced does >> not run at all and a driver relies on the side effect of the hint >> setting the initial affinity. Bah... >> > > Right, but if they only rely on this API so that the IRQs are spread across > all the CPUs then that issue is already resolved and these other drivers > should not regress because of changing this behavior. Isn't it? Is that true for all architectures? >> While none of the drivers (except the perf muck) actually prevents >> userspace from fiddling with the affinity (via IRQF_NOBALANCING) a >> deeper inspection shows that they actually might rely on the current >> behaviour if irqbalanced is disabled. Of course every driver has its own >> convoluted way to do that and all of those functions are well >> documented. What a mess. >> >> If the hint still serves a purpose then we can provide a variant which >> solely applies the hint and does not fiddle with the actual affinity, >> but if the hint is useless anyway then we have a way better option to >> clean that up. >> > > +1 = 1 Thanks, tglx
next prev parent reply other threads:[~2021-05-18 0:04 UTC|newest] Thread overview: 71+ 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 2021-05-01 2:18 ` [Intel-wired-lan] " Jesse Brandeburg 2021-05-04 12:15 ` Robin Murphy 2021-05-04 12:15 ` [Intel-wired-lan] " Robin Murphy 2021-05-04 14:29 ` Nitesh Lal 2021-05-04 14:29 ` [Intel-wired-lan] " Nitesh Lal 2021-05-04 16:23 ` Jesse Brandeburg 2021-05-04 16:23 ` [Intel-wired-lan] " Jesse Brandeburg 2021-05-17 16:57 ` Nitesh Lal 2021-05-17 16:57 ` [Intel-wired-lan] " Nitesh Lal 2021-05-17 17:26 ` Robin Murphy 2021-05-17 17:26 ` [Intel-wired-lan] " Robin Murphy 2021-05-17 18:08 ` Thomas Gleixner 2021-05-17 18:08 ` [Intel-wired-lan] " Thomas Gleixner 2021-05-17 18:50 ` Robin Murphy 2021-05-17 18:50 ` [Intel-wired-lan] " Robin Murphy 2021-05-17 19:08 ` Thomas Gleixner 2021-05-17 19:08 ` [Intel-wired-lan] " Thomas Gleixner 2021-05-17 19:43 ` Thomas Gleixner 2021-05-17 19:43 ` [Intel-wired-lan] " Thomas Gleixner 2021-05-17 20:18 ` Thomas Gleixner 2021-05-17 20:18 ` [Intel-wired-lan] " Thomas Gleixner 2021-05-17 18:21 ` Nitesh Lal 2021-05-17 18:21 ` [Intel-wired-lan] " Nitesh Lal 2021-05-17 19:47 ` Thomas Gleixner 2021-05-17 19:47 ` [Intel-wired-lan] " Thomas Gleixner 2021-05-17 21:13 ` Nitesh Lal 2021-05-17 21:13 ` [Intel-wired-lan] " Nitesh Lal 2021-05-17 20:48 ` Thomas Gleixner 2021-05-17 20:48 ` [Intel-wired-lan] " Thomas Gleixner 2021-05-17 22:44 ` Nitesh Lal 2021-05-17 22:44 ` [Intel-wired-lan] " Nitesh Lal 2021-05-18 0:03 ` Thomas Gleixner [this message] 2021-05-18 0:03 ` Thomas Gleixner 2021-05-18 0:23 ` Nitesh Lal 2021-05-18 0:23 ` [Intel-wired-lan] " Nitesh Lal 2021-05-20 21:57 ` Nitesh Lal 2021-05-20 21:57 ` [Intel-wired-lan] " Nitesh Lal 2021-05-21 0:03 ` Nitesh Lal 2021-05-21 0:03 ` [Intel-wired-lan] " Nitesh Lal 2021-05-21 11:56 ` Thomas Gleixner 2021-05-21 11:56 ` [Intel-wired-lan] " Thomas Gleixner 2021-05-21 12:03 ` [PATCH] genirq: Provide new interfaces for affinity hints Thomas Gleixner 2021-05-21 12:03 ` [Intel-wired-lan] " Thomas Gleixner 2021-05-21 15:45 ` Lijun Pan 2021-05-21 15:45 ` [Intel-wired-lan] " Lijun Pan 2021-05-21 21:45 ` Thomas Gleixner 2021-05-21 21:45 ` [Intel-wired-lan] " Thomas Gleixner 2021-05-21 16:13 ` Nitesh Lal 2021-05-21 16:13 ` [Intel-wired-lan] " Nitesh Lal 2021-05-21 21:48 ` Thomas Gleixner 2021-05-21 21:48 ` [Intel-wired-lan] " Thomas Gleixner 2021-06-04 20:35 ` Nitesh Lal 2021-06-04 20:35 ` [Intel-wired-lan] " Nitesh Lal 2021-05-27 10:03 ` Shung-Hsi Yu 2021-05-27 10:03 ` [Intel-wired-lan] " Shung-Hsi Yu 2021-05-27 10:21 ` Shung-Hsi Yu 2021-05-27 10:21 ` [Intel-wired-lan] " Shung-Hsi Yu 2021-05-27 13:06 ` Nitesh Lal 2021-05-27 13:06 ` [Intel-wired-lan] " Nitesh Lal 2021-05-28 7:20 ` Shung-Hsi Yu 2021-05-28 7:20 ` [Intel-wired-lan] " Shung-Hsi Yu 2021-06-07 17:00 ` Nitesh Lal 2021-06-07 17:00 ` [Intel-wired-lan] " Nitesh Lal 2021-06-14 16:12 ` Nitesh Lal 2021-06-14 16:12 ` [Intel-wired-lan] " 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 13:46 ` [Intel-wired-lan] " Nitesh Lal 2021-05-21 15:15 ` Thomas Gleixner 2021-05-21 15:15 ` [Intel-wired-lan] " 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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