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From: Frederic Weisbecker <frederic@kernel.org>
To: hpa@zytor.com, tglx@linutronix.de, mingo@kernel.org,
	linux-kernel@vger.kernel.org, rafael.j.wysocki@intel.com,
	npiggin@gmail.com, fweisbec@gmail.com, peterz@infradead.org,
	torvalds@linux-foundation.org
Cc: linux-tip-commits@vger.kernel.org
Subject: Re: [tip:sched/core] sched/isolation: Require a present CPU in housekeeping mask
Date: Sat, 4 May 2019 02:27:34 +0200	[thread overview]
Message-ID: <20190504002733.GB19076@lenoir> (raw)
In-Reply-To: <tip-9219565aa89033a9cfdae788c1940473a1253d6c@git.kernel.org>

On Fri, May 03, 2019 at 10:47:37AM -0700, tip-bot for Nicholas Piggin wrote:
> Commit-ID:  9219565aa89033a9cfdae788c1940473a1253d6c
> Gitweb:     https://git.kernel.org/tip/9219565aa89033a9cfdae788c1940473a1253d6c
> Author:     Nicholas Piggin <npiggin@gmail.com>
> AuthorDate: Thu, 11 Apr 2019 13:34:47 +1000
> Committer:  Ingo Molnar <mingo@kernel.org>
> CommitDate: Fri, 3 May 2019 19:42:58 +0200
> 
> sched/isolation: Require a present CPU in housekeeping mask
> 
> During housekeeping mask setup, currently a possible CPU is required.
> That does not guarantee the CPU would be available at boot time, so
> check to ensure that at least one present CPU is in the mask.

I have a doubt about the requirements and semantics of cpu_present_mask.
IIUC a present CPU means that it is physically plugged in (from ACPI
perspective) but might not be logically plugged in (set on cpu_online_mask).

But do we have the guarantee that a present CPU _will_ be online at least once
right after the boot? After all, kernel parameters such as "maxcpus=" can prevent
from turning some CPUs on. I guess there are even more creative ways to achieve
that.

In any case we really require the housekeeper to be forced online. Perhaps
I missed that enforcement somewhere in the patchset?

Thanks.

  parent reply	other threads:[~2019-05-04  0:27 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-04-11  3:34 [PATCH v2 0/5] Allow CPU0 to be nohz full Nicholas Piggin
2019-04-11  3:34 ` [PATCH v2 1/5] sched/core: allow the remote scheduler tick to be started on CPU0 Nicholas Piggin
2019-05-03 11:28   ` [tip:sched/core] sched/core: Allow " tip-bot for Nicholas Piggin
2019-04-11  3:34 ` [PATCH v2 2/5] PM / suspend: add function to disable secondaries for suspend Nicholas Piggin
2019-05-03 11:29   ` [tip:sched/core] power/suspend: Add " tip-bot for Nicholas Piggin
2019-05-03 17:46   ` tip-bot for Nicholas Piggin
2019-04-11  3:34 ` [PATCH v2 3/5] kernel/cpu: Allow non-zero CPU to be primary for suspend / kexec freeze Nicholas Piggin
2019-04-25 12:02   ` Peter Zijlstra
2019-04-26  4:32     ` Nicholas Piggin
2019-05-03 11:29   ` [tip:sched/core] " tip-bot for Nicholas Piggin
2019-05-03 17:46   ` tip-bot for Nicholas Piggin
2019-04-11  3:34 ` [PATCH v2 4/5] kernel/sched/isolation: require a present CPU in housekeeping mask Nicholas Piggin
2019-05-03 11:30   ` [tip:sched/core] sched/isolation: Require " tip-bot for Nicholas Piggin
2019-05-03 17:47   ` tip-bot for Nicholas Piggin
2019-05-03 23:52     ` Frederic Weisbecker
2019-05-04  0:27     ` Frederic Weisbecker [this message]
2019-05-04  6:59       ` Nicholas Piggin
2019-05-06 15:16         ` Frederic Weisbecker
2019-05-06 23:50           ` Nicholas Piggin
2019-05-08  0:35             ` Frederic Weisbecker
2019-05-08  1:38               ` Nicholas Piggin
2019-04-11  3:34 ` [PATCH v2 5/5] nohz_full: Allow the boot CPU to be nohz_full Nicholas Piggin
2019-05-03 11:31   ` [tip:sched/core] " tip-bot for Nicholas Piggin
2019-05-03 17:48   ` tip-bot for Nicholas Piggin
2019-04-25 12:04 ` [PATCH v2 0/5] Allow CPU0 to be nohz full Peter Zijlstra
2019-04-30  2:46   ` Nicholas Piggin
2019-04-30 12:07     ` Peter Zijlstra

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