From: Heiko Carstens <hca@linux.ibm.com>
To: Pierre Morel <pmorel@linux.ibm.com>
Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>,
kvm@vger.kernel.org, linux-s390@vger.kernel.org,
linux-kernel@vger.kernel.org, borntraeger@de.ibm.com,
frankja@linux.ibm.com, cohuck@redhat.com, david@redhat.com,
thuth@redhat.com, gor@linux.ibm.com
Subject: Re: [PATCH v5 1/1] s390x: KVM: accept STSI for CPU topology information
Date: Mon, 13 Dec 2021 16:21:48 +0100 [thread overview]
Message-ID: <YbdlDFLjZzpC6RRd@osiris> (raw)
In-Reply-To: <fbc46b35-10af-2c7e-6e47-e4987070ad83@linux.ibm.com>
On Mon, Dec 13, 2021 at 03:26:58PM +0100, Pierre Morel wrote:
> > Why is this assumption necessary? The statement that Linux runs only
> > with horizontal polarization is not true.
> >
>
> Right, I will rephrase this as:
>
> "Polarization change is not taken into account, QEMU intercepts queries for
> polarization change (PTF) and only provides horizontal polarization
> indication to Guest's Linux."
>
> @Heiko, I did not find any usage of the polarization in the kernel other
> than an indication in the sysfs. Is there currently other use of the
> polarization that I did not see?
You can change polarization by writing to /sys/devices/system/cpu/dispatching.
Or alternativel use the chcpu tool to change polarization. There is
however no real support for vertical polarization implemented in the
kernel. Therefore changing to vertical polarization is _not_
recommended, since it will most likely have negative performance
impacts on your Linux system.
However the interface is still there for experimental purposes.
next prev parent reply other threads:[~2021-12-13 15:21 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-22 13:14 [PATCH v5 0/1] s390x: KVM: CPU Topology Pierre Morel
2021-11-22 13:14 ` [PATCH v5 1/1] s390x: KVM: accept STSI for CPU topology information Pierre Morel
2021-12-07 9:43 ` Pierre Morel
2021-12-09 12:36 ` Claudio Imbrenda
2021-12-09 13:31 ` Pierre Morel
2021-12-09 15:54 ` Heiko Carstens
2021-12-13 10:05 ` Pierre Morel
2021-12-13 14:26 ` Pierre Morel
2021-12-13 15:21 ` Heiko Carstens [this message]
2021-12-13 15:46 ` Pierre Morel
2021-12-09 16:08 ` Janosch Frank
2021-12-13 10:16 ` Pierre Morel
2021-12-14 9:01 ` [PATCH v5 0/1] s390x: KVM: CPU Topology Alexandra Winter
2021-12-16 15:16 ` Pierre Morel
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