From: Daniel Lezcano <daniel.lezcano@linaro.org>
To: Ming Lei <ming.lei@redhat.com>
Cc: Keith Busch <keith.busch@intel.com>,
Hannes Reinecke <hare@suse.com>,
Bart Van Assche <bvanassche@acm.org>,
linux-scsi@vger.kernel.org, Peter Zijlstra <peterz@infradead.org>,
Long Li <longli@microsoft.com>,
John Garry <john.garry@huawei.com>,
LKML <linux-kernel@vger.kernel.org>,
linux-nvme@lists.infradead.org, Jens Axboe <axboe@fb.com>,
Ingo Molnar <mingo@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
Christoph Hellwig <hch@lst.de>, Sagi Grimberg <sagi@grimberg.me>
Subject: Re: [PATCH 1/4] softirq: implement IRQ flood detection mechanism
Date: Fri, 6 Sep 2019 07:14:15 +0200 [thread overview]
Message-ID: <ffefcfa0-09b6-9af5-f94e-8e7ddd2eef16@linaro.org> (raw)
In-Reply-To: <20190906014819.GB27116@ming.t460p>
Hi,
On 06/09/2019 03:48, Ming Lei wrote:
[ ... ]
>> You did not share yet the analysis of the problem (the kernel warnings
>> give the symptoms) and gave the reasoning for the solution. It is hard
>> to understand what you are looking for exactly and how to connect the dots.
>
> Let me explain it one more time:>
> When one IRQ flood happens on one CPU:
>
> 1) softirq handling on this CPU can't make progress
>
> 2) kernel thread bound to this CPU can't make progress
>
> For example, network may require softirq to xmit packets, or another irq
> thread for handling keyboards/mice or whatever, or rcu_sched may depend
> on that CPU for making progress, then the irq flood stalls the whole
> system.
>
>>
>> AFAIU, there are fast medium where the responses to requests are faster
>> than the time to process them, right?
>
> Usually medium may not be faster than CPU, now we are talking about
> interrupts, which can be originated from lots of devices concurrently,
> for example, in Long Li'test, there are 8 NVMe drives involved.
>
>>
>> I don't see how detecting IRQ flooding and use a threaded irq is the
>> solution, can you explain?
>
> When IRQ flood is detected, we reserve a bit little time for providing
> chance to make softirq/threads scheduled by scheduler, then the above
> problem can be avoided.
>
>>
>> If the responses are coming at a very high rate, whatever the solution
>> (interrupts, threaded interrupts, polling), we are still in the same
>> situation.
>
> When we moving the interrupt handling into irq thread, other softirq/
> threaded interrupt/thread gets chance to be scheduled, so we can avoid
> to stall the whole system.
Ok, so the real problem is per-cpu bounded tasks.
I share Thomas opinion about a NAPI like approach.
I do believe you should also rely on the IRQ_TIME_ACCOUNTING (may be get
it optimized) to contribute to the CPU load and enforce task migration
at load balance.
>> My suggestion was initially to see if the interrupt load will be taken
>> into accounts in the cpu load and favorize task migration with the
>> scheduler load balance to a less loaded CPU, thus the CPU processing
>> interrupts will end up doing only that while other CPUs will handle the
>> "threaded" side.
>>
>> Beside that, I'm wondering if the block scheduler should be somehow
>> involved in that [1]
>
> For NVMe or any multi-queue storage, the default scheduler is 'none',
> which basically does nothing except for submitting IO asap.
>
>
> Thanks,
> Ming
>
--
<http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs
Follow Linaro: <http://www.facebook.com/pages/Linaro> Facebook |
<http://twitter.com/#!/linaroorg> Twitter |
<http://www.linaro.org/linaro-blog/> Blog
next prev parent reply other threads:[~2019-09-06 5:14 UTC|newest]
Thread overview: 65+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-27 8:53 [PATCH 0/4] genirq/nvme: add IRQF_RESCUE_THREAD for avoiding IRQ flood Ming Lei
2019-08-27 8:53 ` [PATCH 1/4] softirq: implement IRQ flood detection mechanism Ming Lei
2019-08-27 14:42 ` Thomas Gleixner
2019-08-27 16:19 ` Thomas Gleixner
2019-08-27 23:04 ` Ming Lei
2019-08-27 23:12 ` Thomas Gleixner
2019-08-27 22:58 ` Ming Lei
2019-08-27 23:09 ` Thomas Gleixner
2019-08-28 11:06 ` Ming Lei
2019-08-28 11:23 ` Thomas Gleixner
2019-08-28 13:50 ` Ming Lei
2019-08-28 14:07 ` Thomas Gleixner
2019-09-03 3:30 ` Ming Lei
2019-09-03 5:59 ` Daniel Lezcano
2019-09-03 6:31 ` Ming Lei
2019-09-03 6:40 ` Daniel Lezcano
2019-09-03 7:28 ` Ming Lei
2019-09-03 7:50 ` Daniel Lezcano
2019-09-03 9:30 ` Ming Lei
2019-09-04 17:07 ` Bart Van Assche
2019-09-04 17:31 ` Daniel Lezcano
2019-09-04 17:38 ` Bart Van Assche
2019-09-04 18:02 ` Peter Zijlstra
2019-09-04 19:47 ` Bart Van Assche
2019-09-05 9:11 ` Ming Lei
2019-09-05 9:06 ` Ming Lei
2019-09-05 10:37 ` Daniel Lezcano
2019-09-06 1:22 ` Long Li
2019-09-06 4:36 ` Daniel Lezcano
2019-09-06 4:44 ` Long Li
2019-09-06 1:48 ` Ming Lei
2019-09-06 5:14 ` Daniel Lezcano [this message]
2019-09-06 18:30 ` Sagi Grimberg
2019-09-06 18:52 ` Keith Busch
2019-09-07 0:01 ` Ming Lei
2019-09-10 3:10 ` Sagi Grimberg
2019-09-18 0:00 ` Long Li
2019-09-20 17:14 ` Sagi Grimberg
2019-09-20 19:12 ` Long Li
2019-09-20 20:45 ` Sagi Grimberg
2019-09-24 0:57 ` Long Li
2019-09-18 14:37 ` Ming Lei
2019-09-20 17:09 ` Sagi Grimberg
2019-09-06 14:18 ` Keith Busch
2019-09-06 17:50 ` Long Li
2019-09-06 22:19 ` Ming Lei
2019-09-06 22:25 ` Keith Busch
2019-09-06 23:13 ` Ming Lei
2019-09-10 0:24 ` Ming Lei
2019-09-03 8:09 ` Thomas Gleixner
2019-09-03 9:24 ` Ming Lei
2019-08-29 6:15 ` Long Li
2019-08-30 0:55 ` Ming Lei
2019-08-27 8:53 ` [PATCH 2/4] genirq: add IRQF_RESCUE_THREAD Ming Lei
2019-08-27 8:53 ` [PATCH 3/4] nvme: pci: pass IRQF_RESCURE_THREAD to request_threaded_irq Ming Lei
2019-08-27 9:06 ` Johannes Thumshirn
2019-08-27 9:09 ` Ming Lei
2019-08-27 9:12 ` Johannes Thumshirn
2019-08-27 14:34 ` Keith Busch
2019-08-27 14:44 ` Keith Busch
2019-08-27 15:10 ` Bart Van Assche
2019-08-28 1:45 ` Ming Lei
2019-08-27 8:53 ` [PATCH 4/4] genirq: use irq's affinity for threaded irq with IRQF_RESCUE_THREAD Ming Lei
2019-08-27 14:35 ` Keith Busch
2019-09-06 8:50 ` John Garry
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=ffefcfa0-09b6-9af5-f94e-8e7ddd2eef16@linaro.org \
--to=daniel.lezcano@linaro.org \
--cc=axboe@fb.com \
--cc=bvanassche@acm.org \
--cc=hare@suse.com \
--cc=hch@lst.de \
--cc=john.garry@huawei.com \
--cc=keith.busch@intel.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-nvme@lists.infradead.org \
--cc=linux-scsi@vger.kernel.org \
--cc=longli@microsoft.com \
--cc=ming.lei@redhat.com \
--cc=mingo@redhat.com \
--cc=peterz@infradead.org \
--cc=sagi@grimberg.me \
--cc=tglx@linutronix.de \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).