From: Scott Wood <scottwood@freescale.com>
To: Greg Kurz <gkurz@linux.vnet.ibm.com>
Cc: linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH 2 1/4] powerpc: drop the ability to tweak SMT mode at boot time
Date: Fri, 5 Dec 2014 12:52:45 -0600 [thread overview]
Message-ID: <1417805565.334.15.camel@freescale.com> (raw)
In-Reply-To: <20141205151341.11028.47570.stgit@bahia.lab.toulouse-stg.fr.ibm.com>
On Fri, 2014-12-05 at 16:14 +0100, Greg Kurz wrote:
> The smt-enabled kernel parameter basically leaves unwanted cpus executing
> in firmware or wherever they happen to be. The very same applies to the
> ibm,smt-enabled DT property which is no more used by anything known. These
> are hacks that shoudn't be used in a production environment.
>
> Quoting mpe, "there are better ways for firmware to disable SMT".
Those "better ways" don't apply to Freescale chips, where the OS enables
(or not) SMT without any interaction with firmware. I don't care about
the ibm,smt-enabled property, but can we please keep the smt-enabled
boot option?
> It also has an evil side effect on the split-core feature for powernv. The
> code needs all the cpus to participate to the split mode update: it relies
> on smp_send_reschedule() to get offline ones to do so. This doesn't work with
> cpus that haven't come up... The consequence is a kernel hang on powernv when
> trying to limit the number of hw threads at boot time (e.g. smt-enabled to
> anything but 8 on POWER8).
In that case could you disable the option only on that hardware?
> This patch simply removes both the smt-enabled kernel parameter and the
> ibm,smt-enabled property for all platforms. The new default is to start
> all hw threads. That leaves /sys the only supported API to change SMT
> settings.
How would you use /sys for this? Are you talking about CPU hotplug?
-Scott
next prev parent reply other threads:[~2014-12-05 18:52 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-12-05 15:13 [PATCH 2 0/4] powerpc: don't mess with SMT at boot time Greg Kurz
2014-12-05 15:14 ` [PATCH 2 1/4] powerpc: drop the ability to tweak SMT mode " Greg Kurz
2014-12-05 18:52 ` Scott Wood [this message]
2014-12-08 8:23 ` Greg Kurz
2014-12-08 22:39 ` Scott Wood
2014-12-09 4:11 ` Michael Ellerman
2014-12-09 8:53 ` Greg Kurz
2014-12-09 21:04 ` Scott Wood
2014-12-09 23:56 ` Michael Ellerman
2014-12-10 0:14 ` Scott Wood
2014-12-10 2:14 ` Michael Ellerman
2014-12-10 23:50 ` Scott Wood
2014-12-12 5:19 ` Michael Ellerman
2014-12-05 15:14 ` [PATCH 2 2/4] powerpc: drop smt_enabled_at_boot Greg Kurz
2014-12-05 15:15 ` [PATCH 2 3/4] powerpc: drop smp_generic_cpu_bootable() Greg Kurz
2014-12-05 15:34 ` Greg Kurz
2014-12-05 15:15 ` [PATCH 2 4/4] powerpc: drop the cpu_bootable hook Greg Kurz
2014-12-05 15:42 ` [PATCH] " Greg Kurz
2014-12-12 5:22 ` [PATCH 2 0/4] powerpc: don't mess with SMT at boot time Michael Ellerman
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=1417805565.334.15.camel@freescale.com \
--to=scottwood@freescale.com \
--cc=gkurz@linux.vnet.ibm.com \
--cc=linuxppc-dev@lists.ozlabs.org \
/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).