From: Nathan Lynch <nathanl@linux.ibm.com>
To: "Gautham R. Shenoy" <ego@linux.vnet.ibm.com>
Cc: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
Michael Ellerman <mpe@ellerman.id.au>,
Nicholas Piggin <npiggin@gmail.com>,
Tyrel Datwyler <tyreld@linux.ibm.com>,
Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>,
Kamalesh Babulal <kamaleshb@in.ibm.com>,
"Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>,
"Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Subject: Re: [PATCH v2 1/1] pseries/hotplug-cpu: Change default behaviour of cede_offline to "off"
Date: Thu, 31 Oct 2019 11:30:11 -0500 [thread overview]
Message-ID: <87k18klvxo.fsf@linux.ibm.com> (raw)
In-Reply-To: <1571740391-3251-2-git-send-email-ego@linux.vnet.ibm.com>
"Gautham R. Shenoy" <ego@linux.vnet.ibm.com> writes:
> From: "Gautham R. Shenoy" <ego@linux.vnet.ibm.com>
>
> Currently on PSeries Linux guests, the offlined CPU can be put to one
> of the following two states:
> - Long term processor cede (also called extended cede)
> - Returned to the hypervisor via RTAS "stop-self" call.
>
> This is controlled by the kernel boot parameter "cede_offline=on/off".
>
> By default the offlined CPUs enter extended cede. The PHYP hypervisor
> considers CPUs in extended cede to be "active" since they are still
> under the control fo the Linux guests. Hence, when we change the SMT
> modes by offlining the secondary CPUs, the PURR and the RWMR SPRs will
> continue to count the values for offlined CPUs in extended cede as if
> they are online. This breaks the accounting in tools such as lparstat.
>
> To fix this, ensure that by default the offlined CPUs are returned to
> the hypervisor via RTAS "stop-self" call by changing the default value
> of "cede_offline_enabled" to false.
>
> Fixes: commit 3aa565f53c39 ("powerpc/pseries: Add hooks to put the CPU
> into an appropriate offline state")
>
> Signed-off-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>
I'm OK with changing the default as a precursor to removing the code
that implements the cede offline mode.
Acked-by: Nathan Lynch <nathanl@linux.ibm.com>
next prev parent reply other threads:[~2019-10-31 16:30 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-22 10:33 [PATCH v2 0/1] pseries/hotplug: Change the default behaviour of cede_offline Gautham R. Shenoy
2019-10-22 10:33 ` [PATCH v2 1/1] pseries/hotplug-cpu: Change default behaviour of cede_offline to "off" Gautham R. Shenoy
2019-10-31 16:30 ` Nathan Lynch [this message]
2019-10-25 23:03 ` [PATCH v2 0/1] pseries/hotplug: Change the default behaviour of cede_offline Nathan Lynch
2019-10-29 11:13 ` Gautham R Shenoy
2019-10-29 15:29 ` Nathan Lynch
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