From: Long Li <longli@microsoft.com>
To: Ming Lei <ming.lei@redhat.com>, Sagi Grimberg <sagi@grimberg.me>
Cc: "longli@linuxonhyperv.com" <longli@linuxonhyperv.com>,
Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Keith Busch <keith.busch@intel.com>, Jens Axboe <axboe@fb.com>,
Christoph Hellwig <hch@lst.de>,
"linux-nvme@lists.infradead.org" <linux-nvme@lists.infradead.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Hannes Reinecke <hare@suse.com>,
"linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>,
"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>
Subject: RE: [PATCH 3/3] nvme: complete request in work queue on CPU with flooded interrupts
Date: Sat, 24 Aug 2019 00:27:18 +0000 [thread overview]
Message-ID: <CY4PR21MB074173E79C7FC3AC13C69CB3CEA70@CY4PR21MB0741.namprd21.prod.outlook.com> (raw)
In-Reply-To: <20190823032129.GA18680@ming.t460p>
>>>Subject: Re: [PATCH 3/3] nvme: complete request in work queue on CPU
>>>with flooded interrupts
>>>
>>>On Tue, Aug 20, 2019 at 10:33:38AM -0700, Sagi Grimberg wrote:
>>>>
>>>> > From: Long Li <longli@microsoft.com>
>>>> >
>>>> > When a NVMe hardware queue is mapped to several CPU queues, it is
>>>> > possible that the CPU this hardware queue is bound to is flooded by
>>>> > returning I/O for other CPUs.
>>>> >
>>>> > For example, consider the following scenario:
>>>> > 1. CPU 0, 1, 2 and 3 share the same hardware queue 2. the hardware
>>>> > queue interrupts CPU 0 for I/O response 3. processes from CPU 1, 2
>>>> > and 3 keep sending I/Os
>>>> >
>>>> > CPU 0 may be flooded with interrupts from NVMe device that are I/O
>>>> > responses for CPU 1, 2 and 3. Under heavy I/O load, it is possible
>>>> > that CPU 0 spends all the time serving NVMe and other system
>>>> > interrupts, but doesn't have a chance to run in process context.
>>>> >
>>>> > To fix this, CPU 0 can schedule a work to complete the I/O request
>>>> > when it detects the scheduler is not making progress. This serves
>>>multiple purposes:
>>>> >
>>>> > 1. This CPU has to be scheduled to complete the request. The other
>>>> > CPUs can't issue more I/Os until some previous I/Os are completed.
>>>> > This helps this CPU get out of NVMe interrupts.
>>>> >
>>>> > 2. This acts a throttling mechanisum for NVMe devices, in that it
>>>> > can not starve a CPU while servicing I/Os from other CPUs.
>>>> >
>>>> > 3. This CPU can make progress on RCU and other work items on its
>>>queue.
>>>>
>>>> The problem is indeed real, but this is the wrong approach in my mind.
>>>>
>>>> We already have irqpoll which takes care proper budgeting polling
>>>> cycles and not hogging the cpu.
>>>
>>>The issue isn't unique to NVMe, and can be any fast devices which
>>>interrupts CPU too frequently, meantime the interrupt/softirq handler may
>>>take a bit much time, then CPU is easy to be lockup by the interrupt/sofirq
>>>handler, especially in case that multiple submission CPUs vs. single
>>>completion CPU.
>>>
>>>Some SCSI devices has the same problem too.
>>>
>>>Could we consider to add one generic mechanism to cover this kind of
>>>problem?
>>>
>>>One approach I thought of is to allocate one backup thread for handling such
>>>interrupt, which can be marked as IRQF_BACKUP_THREAD by drivers.
>>>
>>>Inside do_IRQ(), irqtime is accounted, before calling action->handler(),
>>>check if this CPU has taken too long time for handling IRQ(interrupt or
>>>softirq) and see if this CPU could be lock up. If yes, wakeup the backup
How do you know if this CPU is spending all the time in do_IRQ()?
Is it something like:
If (IRQ_time /elapsed_time > a threshold value)
wake up the backup thread
>>>thread to handle the interrupt for avoiding lockup this CPU.
>>>
>>>The threaded interrupt framework is there, and this way could be easier to
>>>implement. Meantime most time the handler is run in interrupt context and
>>>we may avoid the performance loss when CPU isn't busy enough.
>>>
>>>Any comment on this approach?
>>>
>>>Thanks,
>>>Ming
next prev parent reply other threads:[~2019-08-24 0:27 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-20 6:14 [PATCH 0/3] fix interrupt swamp in NVMe longli
2019-08-20 6:14 ` [PATCH 1/3] sched: define a function to report the number of context switches on a CPU longli
2019-08-20 9:38 ` Peter Zijlstra
2019-08-21 8:20 ` Long Li
2019-08-21 10:34 ` Peter Zijlstra
2019-08-20 9:39 ` Peter Zijlstra
2019-08-20 6:14 ` [PATCH 2/3] sched: export idle_cpu() longli
2019-08-20 6:14 ` [PATCH 3/3] nvme: complete request in work queue on CPU with flooded interrupts longli
2019-08-20 9:52 ` Peter Zijlstra
2019-08-21 8:37 ` Long Li
2019-08-21 10:35 ` Peter Zijlstra
2019-08-20 17:33 ` Sagi Grimberg
2019-08-21 8:39 ` Long Li
2019-08-21 17:36 ` Long Li
2019-08-21 21:54 ` Sagi Grimberg
2019-08-24 0:13 ` Long Li
2019-08-23 3:21 ` Ming Lei
2019-08-24 0:27 ` Long Li [this message]
2019-08-24 12:55 ` Ming Lei
2019-08-20 8:25 ` [PATCH 0/3] fix interrupt swamp in NVMe Ming Lei
2019-08-20 8:59 ` John Garry
2019-08-20 15:05 ` Keith Busch
2019-08-21 7:47 ` Long Li
2019-08-21 9:44 ` Ming Lei
2019-08-21 10:03 ` John Garry
2019-08-21 16:27 ` Long Li
2019-08-22 1:33 ` Ming Lei
2019-08-22 2:00 ` Keith Busch
2019-08-22 2:23 ` Ming Lei
2019-08-22 9:48 ` Thomas Gleixner
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=CY4PR21MB074173E79C7FC3AC13C69CB3CEA70@CY4PR21MB0741.namprd21.prod.outlook.com \
--to=longli@microsoft.com \
--cc=axboe@fb.com \
--cc=hare@suse.com \
--cc=hch@lst.de \
--cc=keith.busch@intel.com \
--cc=linux-block@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-nvme@lists.infradead.org \
--cc=linux-scsi@vger.kernel.org \
--cc=longli@linuxonhyperv.com \
--cc=ming.lei@redhat.com \
--cc=mingo@redhat.com \
--cc=peterz@infradead.org \
--cc=sagi@grimberg.me \
/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).