From: Marcelo Tosatti <mtosatti@redhat.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Robin Murphy <robin.murphy@arm.com>,
Nitesh Narayan Lal <nitesh@redhat.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, 28 Jan 2021 13:33:33 -0300 [thread overview]
Message-ID: <20210128163333.GA38339@fuller.cnet> (raw)
In-Reply-To: <87tur1cay0.fsf@nanos.tec.linutronix.de>
On Thu, Jan 28, 2021 at 04:56:07PM +0100, Thomas Gleixner wrote:
> On Wed, Jan 27 2021 at 10:09, Marcelo Tosatti wrote:
> > On Wed, Jan 27, 2021 at 12:36:30PM +0000, Robin Murphy wrote:
> >> > > > /**
> >> > > > * cpumask_next - get the next cpu in a cpumask
> >> > > > @@ -205,22 +206,27 @@ void __init free_bootmem_cpumask_var(cpumask_var_t mask)
> >> > > > */
> >> > > > unsigned int cpumask_local_spread(unsigned int i, int node)
> >> > > > {
> >> > > > - int cpu;
> >> > > > + int cpu, hk_flags;
> >> > > > + const struct cpumask *mask;
> >> > > > + hk_flags = HK_FLAG_DOMAIN | HK_FLAG_MANAGED_IRQ;
> >> > > > + mask = housekeeping_cpumask(hk_flags);
> >> > >
> >> > > AFAICS, this generally resolves to something based on cpu_possible_mask
> >> > > rather than cpu_online_mask as before, so could now potentially return an
> >> > > offline CPU. Was that an intentional change?
> >> >
> >> > Robin,
> >> >
> >> > AFAICS online CPUs should be filtered.
> >>
> >> Apologies if I'm being thick, but can you explain how? In the case of
> >> isolation being disabled or compiled out, housekeeping_cpumask() is
> >> literally just "return cpu_possible_mask;". If we then iterate over that
> >> with for_each_cpu() and just return the i'th possible CPU (e.g. in the
> >> NUMA_NO_NODE case), what guarantees that CPU is actually online?
> >>
> >> Robin.
> >
> > Nothing, but that was the situation before 1abdfe706a579a702799fce465bceb9fb01d407c
> > as well.
> >
> > cpumask_local_spread() should probably be disabling CPU hotplug.
>
> It can't unless all callers are from preemtible code.
>
> Aside of that this whole frenzy to sprinkle housekeeping_cpumask() all
> over the kernel is just wrong, really.
>
> As I explained several times before there are very valid reasons for
> having queues and interrupts on isolated CPUs. Just optimizing for the
> usecases some people care about is not making anything better.
And that is right.
next prev parent reply other threads:[~2021-01-28 17:02 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 [this message]
[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
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=20210128163333.GA38339@fuller.cnet \
--to=mtosatti@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=nitesh@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).