From: Nitesh Narayan Lal <nitesh@redhat.com>
To: Thomas Gleixner <tglx@linutronix.de>,
Marcelo Tosatti <mtosatti@redhat.com>
Cc: Robin Murphy <robin.murphy@arm.com>,
linux-kernel@vger.kernel.org, linux-api@vger.kernel.org,
frederic@kernel.org, juri.lelli@redhat.com, abelits@marvell.com,
bhelgaas@google.com, linux-pci@vger.kernel.org,
rostedt@goodmis.org, mingo@kernel.org, peterz@infradead.org,
davem@davemloft.net, akpm@linux-foundation.org,
sfr@canb.auug.org.au, stephen@networkplumber.org,
rppt@linux.vnet.ibm.com, jinyuqi@huawei.com,
zhangshaokun@hisilicon.com
Subject: Re: [Patch v4 1/3] lib: Restrict cpumask_local_spread to houskeeping CPUs
Date: Thu, 11 Feb 2021 10:55:17 -0500 [thread overview]
Message-ID: <7780ae60-efbd-2902-caaa-0249a1f277d9@redhat.com> (raw)
In-Reply-To: <d0aed683-87ae-91a2-d093-de3f5d8a8251@redhat.com>
On 2/6/21 7:43 PM, Nitesh Narayan Lal wrote:
> On 2/5/21 5:23 PM, Thomas Gleixner wrote:
>> On Thu, Feb 04 2021 at 14:17, Nitesh Narayan Lal wrote:
>>> On 2/4/21 2:06 PM, Marcelo Tosatti wrote:
>>>>>> How about adding a new flag for isolcpus instead?
>>>>>>
>>>>> Do you mean a flag based on which we can switch the affinity mask to
>>>>> housekeeping for all the devices at the time of IRQ distribution?
>>>> Yes a new flag for isolcpus. HK_FLAG_IRQ_SPREAD or some better name.
>>> Does sounds like a nice idea to explore, lets see what Thomas thinks about it.
<snip>
>>> When the affinity mask of the interrupt at the time when it is actually
>>> requested contains an isolated CPU then nothing prevents the kernel from
>>> steering it at an isolated CPU. But that has absolutely nothing to do
>>> with that spreading thingy.
>>>
>>> The only difference which this change makes is the fact that the
>>> affinity hint changes. Nothing else.
>>>
> Thanks for the detailed explanation.
>
> Before I posted this patch, I was doing some debugging on a setup where I
> was observing some latency issues due to the iavf IRQs that were pinned on
> the isolated CPUs.
>
> Based on some initial traces I had this impression that the affinity hint
> or cpumask_local_spread was somehow playing a role in deciding the affinity
> mask of these IRQs. Although, that does look incorrect after going through
> your explanation.
> For some reason, with a kernel that had this patch when I tried creating
> VFs iavf IRQs always ended up on the HK CPUs.
>
> The reasoning for the above is still not very clear to me. I will investigate
> this further to properly understand this behavior.
>
>
After a little more digging, I found out why cpumask_local_spread change
affects the general/initial smp_affinity for certain device IRQs.
After the introduction of the commit:
e2e64a932 genirq: Set initial affinity in irq_set_affinity_hint()
For all the drivers that set hint, initial affinity is set based on the
CPU retrieved from cpumask_local_spread. So in an environment where
irqbalance is disabled, these device IRQs remain on the CPUs that are
picked from cpumask_local_spread even though they are isolated. I think
the commit message of the reverted patch should have covered this as
well.
--
Thanks
Nitesh
next prev parent reply other threads:[~2021-02-11 16:00 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-25 22:34 [PATCH v4 0/3] Preventing job distribution to isolated CPUs Nitesh Narayan Lal
2020-06-25 22:34 ` [Patch v4 1/3] lib: Restrict cpumask_local_spread to houskeeping CPUs Nitesh Narayan Lal
2020-06-29 16:11 ` Nitesh Narayan Lal
2020-07-01 0:32 ` Andrew Morton
2020-07-01 0:47 ` Nitesh Narayan Lal
2021-01-27 11:57 ` Robin Murphy
2021-01-27 12:19 ` Marcelo Tosatti
2021-01-27 12:36 ` Robin Murphy
2021-01-27 13:09 ` Marcelo Tosatti
2021-01-27 13:49 ` Robin Murphy
2021-01-27 14:16 ` Nitesh Narayan Lal
2021-01-28 15:56 ` Thomas Gleixner
2021-01-28 16:33 ` Marcelo Tosatti
[not found] ` <02ac9d85-7ddd-96da-1252-4663feea7c9f@marvell.com>
2021-02-01 17:50 ` [EXT] " Marcelo Tosatti
2021-01-28 16:02 ` Thomas Gleixner
2021-01-28 16:59 ` Marcelo Tosatti
2021-01-28 17:35 ` Nitesh Narayan Lal
2021-01-28 20:01 ` Thomas Gleixner
[not found] ` <d2a4dc97-a9ed-e0e7-3b9c-c56ae46f6608@redhat.com>
[not found] ` <20210129142356.GB40876@fuller.cnet>
2021-01-29 17:34 ` [EXT] " Alex Belits
[not found] ` <18584612-868c-0f88-5de2-dc93c8638816@redhat.com>
2021-02-05 19:56 ` Thomas Gleixner
2021-02-04 18:15 ` Marcelo Tosatti
2021-02-04 18:47 ` Nitesh Narayan Lal
2021-02-04 19:06 ` Marcelo Tosatti
2021-02-04 19:17 ` Nitesh Narayan Lal
2021-02-05 22:23 ` Thomas Gleixner
2021-02-05 22:26 ` Thomas Gleixner
2021-02-07 0:43 ` Nitesh Narayan Lal
2021-02-11 15:55 ` Nitesh Narayan Lal [this message]
2021-03-04 18:15 ` Nitesh Narayan Lal
[not found] ` <faa8d84e-db67-7fbe-891e-f4987f106b20@marvell.com>
2021-03-04 23:23 ` [EXT] " Nitesh Narayan Lal
2021-04-06 17:22 ` Jesse Brandeburg
2021-04-07 15:18 ` Nitesh Narayan Lal
2021-04-08 18:49 ` Nitesh Narayan Lal
2021-04-14 16:11 ` Jesse Brandeburg
2021-04-15 22:11 ` Nitesh Narayan Lal
2021-04-29 21:44 ` Nitesh Lal
2021-04-30 1:48 ` Jesse Brandeburg
2021-04-30 13:10 ` Nitesh Lal
2021-04-30 7:10 ` Thomas Gleixner
2021-04-30 16:14 ` Nitesh Lal
2021-04-30 18:21 ` Thomas Gleixner
2021-04-30 21:07 ` Nitesh Lal
2021-05-01 2:21 ` Jesse Brandeburg
2021-05-03 13:15 ` Nitesh Lal
2020-06-25 22:34 ` [Patch v4 2/3] PCI: Restrict probe functions to housekeeping CPUs Nitesh Narayan Lal
2020-06-25 22:34 ` [Patch v4 3/3] net: Restrict receive packets queuing " Nitesh Narayan Lal
2020-06-26 11:14 ` Peter Zijlstra
2020-06-26 17:20 ` David Miller
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=7780ae60-efbd-2902-caaa-0249a1f277d9@redhat.com \
--to=nitesh@redhat.com \
--cc=abelits@marvell.com \
--cc=akpm@linux-foundation.org \
--cc=bhelgaas@google.com \
--cc=davem@davemloft.net \
--cc=frederic@kernel.org \
--cc=jinyuqi@huawei.com \
--cc=juri.lelli@redhat.com \
--cc=linux-api@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-pci@vger.kernel.org \
--cc=mingo@kernel.org \
--cc=mtosatti@redhat.com \
--cc=peterz@infradead.org \
--cc=robin.murphy@arm.com \
--cc=rostedt@goodmis.org \
--cc=rppt@linux.vnet.ibm.com \
--cc=sfr@canb.auug.org.au \
--cc=stephen@networkplumber.org \
--cc=tglx@linutronix.de \
--cc=zhangshaokun@hisilicon.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
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).