From: Marc Zyngier <email@example.com> To: John Garry <firstname.lastname@example.org> Cc: Ming Lei <email@example.com>, <firstname.lastname@example.org>, <email@example.com>, <firstname.lastname@example.org>, <email@example.com>, <firstname.lastname@example.org>, <email@example.com>, <firstname.lastname@example.org>, <email@example.com>, <firstname.lastname@example.org>, <email@example.com> Subject: Re: [PATCH RFC 1/1] genirq: Make threaded handler use irq affinity for managed interrupt Date: Tue, 10 Dec 2019 11:36:50 +0000 Message-ID: <firstname.lastname@example.org> (raw) In-Reply-To: <email@example.com> On 2019-12-10 10:59, John Garry wrote: >>> >>> There is no lockup, just a potential performance boost in this >>> change. >>> >>> My colleague Xiang Chen can provide specifics of the test, as he is >>> the one running it. >>> >>> But one key bit of info - which I did not think most relevant >>> before >>> - that is we have 2x SAS controllers running the throughput test on >>> the same host. >>> >>> As such, the completion queue interrupts would be spread >>> identically >>> over the CPUs for each controller. I notice that ARM GICv3 ITS >>> interrupt controller (which we use) does not use the generic irq >>> matrix allocator, which I think would really help with this. >>> >>> Hi Marc, >>> >>> Is there any reason for which we couldn't utilise of the generic >>> irq >>> matrix allocator for GICv3? >> > > Hi Marc, > >> For a start, the ITS code predates the matrix allocator by about >> three >> years. Also, my understanding of this allocator is that it allows >> x86 to cope with a very small number of possible interrupt vectors >> per CPU. The ITS doesn't have such issue, as: >> 1) the namespace is global, and not per CPU >> 2) the namespace is *huge* >> Now, what property of the matrix allocator is the ITS code missing? >> I'd be more than happy to improve it. > > I think specifically the property that the matrix allocator will try > to find a CPU for irq affinity which "has the lowest number of > managed > IRQs allocated" - I'm quoting the comment on > matrix_find_best_cpu_managed(). But that decision is due to allocation constraints. You can have at most 256 interrupts per CPU, so the allocator tries to balance it. On the contrary, the ITS does care about how many interrupt target any given CPU. The whole 2^24 interrupt namespace can be thrown at a single CPU. > The ITS code will make the lowest online CPU in the affinity mask the > target CPU for the interrupt, which may result in some CPUs handling > so many interrupts. If what you want is for the *default* affinity to be spread around, that should be achieved pretty easily. Let me have a think about how to do that. M. -- Jazz is not dead. It just smells funny...
next prev parent reply index Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-12-06 14:35 [PATCH RFC 0/1] Threaded handler uses irq affinity for when the interrupt is managed John Garry 2019-12-06 14:35 ` [PATCH RFC 1/1] genirq: Make threaded handler use irq affinity for managed interrupt John Garry 2019-12-06 15:22 ` Marc Zyngier 2019-12-06 16:16 ` John Garry 2019-12-07 8:03 ` Ming Lei 2019-12-09 14:30 ` John Garry 2019-12-09 15:09 ` Hannes Reinecke 2019-12-09 15:17 ` Marc Zyngier 2019-12-09 15:25 ` Hannes Reinecke 2019-12-09 15:36 ` Marc Zyngier 2019-12-09 15:49 ` Qais Yousef 2019-12-09 15:55 ` Marc Zyngier 2019-12-10 1:43 ` Ming Lei 2019-12-10 9:45 ` John Garry 2019-12-10 10:06 ` Ming Lei 2019-12-10 10:28 ` Marc Zyngier 2019-12-10 10:59 ` John Garry 2019-12-10 11:36 ` Marc Zyngier [this message] 2019-12-10 12:05 ` John Garry 2019-12-10 18:32 ` Marc Zyngier 2019-12-11 9:41 ` John Garry 2019-12-13 10:07 ` John Garry 2019-12-13 10:31 ` Marc Zyngier 2019-12-13 12:08 ` John Garry 2019-12-14 10:59 ` Marc Zyngier 2019-12-11 17:09 ` John Garry 2019-12-12 22:38 ` Ming Lei 2019-12-13 11:12 ` John Garry 2019-12-13 13:18 ` Ming Lei 2019-12-13 15:43 ` John Garry 2019-12-13 17:12 ` Ming Lei 2019-12-13 17:50 ` John Garry 2019-12-14 13:56 ` Marc Zyngier 2019-12-16 10:47 ` John Garry 2019-12-16 11:40 ` Marc Zyngier 2019-12-16 14:17 ` John Garry 2019-12-16 18:00 ` Marc Zyngier 2019-12-16 18:50 ` John Garry 2019-12-20 11:30 ` John Garry 2019-12-20 14:43 ` Marc Zyngier 2019-12-20 15:38 ` John Garry 2019-12-20 16:16 ` Marc Zyngier 2019-12-20 23:31 ` Ming Lei 2019-12-23 9:07 ` Marc Zyngier 2019-12-23 10:26 ` John Garry 2019-12-23 10:47 ` Marc Zyngier 2019-12-23 11:35 ` John Garry 2019-12-24 1:59 ` Ming Lei 2019-12-24 11:20 ` Marc Zyngier 2019-12-25 0:48 ` Ming Lei 2020-01-02 10:35 ` John Garry 2020-01-03 0:46 ` Ming Lei 2020-01-03 10:41 ` John Garry 2020-01-03 11:29 ` Ming Lei 2020-01-03 11:50 ` John Garry 2020-01-04 12:03 ` Ming Lei 2020-05-30 7:46 ` [tip: irq/core] irqchip/gic-v3-its: Balance initial LPI affinity across CPUs tip-bot2 for Marc Zyngier
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