LKML Archive on lore.kernel.org
 help / color / Atom feed
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>,
	Zhang Yi <yi.zhang@redhat.com>
Subject: Re: [PATCH RFC 1/1] genirq: Make threaded handler use irq affinity  for managed interrupt
Date: Tue, 24 Dec 2019 11:20:25 +0000
Message-ID: <7a961950624c414bb9d0c11c914d5c62@www.loen.fr> (raw)
In-Reply-To: <20191224015926.GC13083@ming.t460p>

On 2019-12-24 01:59, Ming Lei wrote:
> On Mon, Dec 23, 2019 at 10:47:07AM +0000, Marc Zyngier wrote:
>> On 2019-12-23 10:26, John Garry wrote:
>> > > > > > 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.
>> >
>> > So I tested v5.5-rc3 with and without the SMMU enabled, and 
>> without
>> > the SMMU enabled I don't get the lockup.
>>
>> OK, so my hunch wasn't completely off... At least we have something
>> to look into.
>>
>> [...]
>>
>> > Obviously this is not conclusive, especially with such limited
>> > testing - 5 minute runs each. The CPU load goes up when disabling 
>> the
>> > SMMU, but that could be attributed to extra throughput (1183K ->
>> > 1539K) loading.
>> >
>> > I do notice that since we complete the NVMe request in irq 
>> context,
>> > we also do the DMA unmap, i.e. talk to the SMMU, in the same 
>> context,
>> > which is less than ideal.
>>
>> It depends on how much overhead invalidating the TLB adds to the
>> equation, but we should be able to do some tracing and find out.
>>
>> > I need to finish for the Christmas break today, so can't check 
>> this
>> > much further ATM.
>>
>> No worries. May I suggest creating a new thread in the new year, 
>> maybe
>> involving Robin and Will as well?
>
> Zhang Yi has observed the CPU lockup issue once when running heavy IO 
> on
> single nvme drive, and please CC him if you have new patch to try.

On which architecture? John was indicating that this also happen on 
x86.

> Then looks the DMA unmap cost is too big on aarch64 if SMMU is 
> involved.

So far, we don't have any data suggesting that this is actually the 
case.
Also, other workloads (such as networking) do not exhibit this 
behaviour,
while being least as unmap-heavy as NVMe is.

If the cross-architecture aspect is confirmed, this points more into
the direction of an interaction between the NVMe subsystem and the
DMA API more than an architecture-specific problem.

Given that we have so far very little data, I'd hold off any 
conclusion.

         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
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 [this message]
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

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=7a961950624c414bb9d0c11c914d5c62@www.loen.fr \
    --to=maz@kernel.org \
    --cc=axboe@kernel.dk \
    --cc=bigeasy@linutronix.de \
    --cc=bvanassche@acm.org \
    --cc=chenxiang66@hisilicon.com \
    --cc=hare@suse.com \
    --cc=hch@lst.de \
    --cc=john.garry@huawei.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=ming.lei@redhat.com \
    --cc=mingo@redhat.com \
    --cc=peterz@infradead.org \
    --cc=tglx@linutronix.de \
    --cc=yi.zhang@redhat.com \
    /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

LKML Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/lkml/0 lkml/git/0.git
	git clone --mirror https://lore.kernel.org/lkml/1 lkml/git/1.git
	git clone --mirror https://lore.kernel.org/lkml/2 lkml/git/2.git
	git clone --mirror https://lore.kernel.org/lkml/3 lkml/git/3.git
	git clone --mirror https://lore.kernel.org/lkml/4 lkml/git/4.git
	git clone --mirror https://lore.kernel.org/lkml/5 lkml/git/5.git
	git clone --mirror https://lore.kernel.org/lkml/6 lkml/git/6.git
	git clone --mirror https://lore.kernel.org/lkml/7 lkml/git/7.git
	git clone --mirror https://lore.kernel.org/lkml/8 lkml/git/8.git
	git clone --mirror https://lore.kernel.org/lkml/9 lkml/git/9.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 lkml lkml/ https://lore.kernel.org/lkml \
		linux-kernel@vger.kernel.org
	public-inbox-index lkml

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-kernel


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git