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From: Marc Zyngier <maz@kernel.org>
To: Ming Lei <ming.lei@redhat.com>
Cc: John Garry <john.garry@huawei.com>, <tglx@linutronix.de>,
	"chenxiang (M)" <chenxiang66@hisilicon.com>,
	<bigeasy@linutronix.de>, <linux-kernel@vger.kernel.org>,
	<hare@suse.com>, <hch@lst.de>, <axboe@kernel.dk>,
	<bvanassche@acm.org>, <peterz@infradead.org>, <mingo@redhat.com>
Subject: Re: [PATCH RFC 1/1] genirq: Make threaded handler use irq affinity  for managed interrupt
Date: Mon, 23 Dec 2019 09:07:39 +0000
Message-ID: <fffcd23dd8286615b6e2c99620836cb1@www.loen.fr> (raw)
In-Reply-To: <20191220233138.GB12403@ming.t460p>

On 2019-12-20 23:31, Ming Lei wrote:
> On Fri, Dec 20, 2019 at 03:38:24PM +0000, John Garry wrote:
>> > > We've got some more results and it looks promising.
>> > >
>> > > So with your patch we get a performance boost of 3180.1K -> 
>> 3294.9K
>> > > IOPS in the D06 SAS env. Then when we change the driver to use
>> > > threaded interrupt handler (mainline currently uses tasklet), we 
>> get a
>> > > boost again up to 3415K IOPS.
>> > >
>> > > Now this is essentially the same figure we had with using 
>> threaded
>> > > handler + the gen irq change in spreading the handler CPU 
>> affinity. We
>> > > did also test your patch + gen irq change and got a performance 
>> drop,
>> > > to 3347K IOPS.
>> > >
>> > > So tentatively I'd say your patch may be all we need.
>> >
>> > OK.
>> >
>> > > FYI, here is how the effective affinity is looking for both SAS
>> > > controllers with your patch:
>> > >
>> > > 74:02.0
>> > > irq 81, cpu list 24-29, effective list 24 cq
>> > > irq 82, cpu list 30-35, effective list 30 cq
>> >
>> > Cool.
>> >
>> > [...]
>> >
>> > > As for your patch itself, I'm still concerned of possible 
>> regressions
>> > > if we don't apply this effective interrupt affinity spread 
>> policy to
>> > > only managed interrupts.
>> >
>> > I'll try and revise that as I post the patch, probably at some 
>> point
>> > between now and Christmas. I still think we should find a way to
>> > address this for the D05 SAS driver though, maybe by managing the
>> > affinity yourself in the driver. But this requires 
>> experimentation.
>>
>> I've already done something experimental for the driver to manage 
>> the
>> affinity, and performance is generally much better:
>>
>> 
>> https://github.com/hisilicon/kernel-dev/commit/e15bd404ed1086fed44da34ed3bd37a8433688a7
>>
>> But I still think it's wise to only consider managed interrupts for 
>> now.
>>
>> >
>> > > JFYI, about NVMe CPU lockup issue, there are 2 works on going 
>> here:
>> > >
>> > > 
>> https://lore.kernel.org/linux-nvme/20191209175622.1964-1-kbusch@kernel.org/T/#t
>> > >
>> > >
>> > > 
>> https://lore.kernel.org/linux-block/20191218071942.22336-1-ming.lei@redhat.com/T/#t
>> > >
>> >
>> > I've also managed to trigger some of them now that I have access 
>> to
>> > a decent box with nvme storage.
>>
>> I only have 2x NVMe SSDs when this occurs - I should not be hitting 
>> this...
>>
>> Out of curiosity, have you tried
>> > with the SMMU disabled? I'm wondering whether we hit some livelock
>> > condition on unmapping buffers...
>>
>> No, but I can give it a try. Doing that should lower the CPU usage, 
>> though,
>> so maybe masks the issue - probably not.
>
> Lots of CPU lockup can is performance issue if there isn't obvious 
> bug.
>
> I am wondering if you may explain it a bit why enabling SMMU may save
> CPU a it?

The other way around. mapping/unmapping IOVAs doesn't comes for free.
I'm trying to find out whether the NVMe map/unmap patterns trigger
something unexpected in the SMMU driver, but that's a very long shot.

         M.
-- 
Jazz is not dead. It just smells funny...

  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
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 [this message]
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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