* Re: [PATCH 1/3] arm: ls1: add CPU hotplug platform support [not found] ` <20140926132038.GF7422@leverpostej> @ 2014-09-28 10:57 ` Li Yang 2014-09-28 14:27 ` Russell King - ARM Linux 0 siblings, 1 reply; 2+ messages in thread From: Li Yang @ 2014-09-28 10:57 UTC (permalink / raw) To: Mark Rutland Cc: Russell King - ARM Linux, Chenhui Zhao, kernel@pengutronix.de, linux-kernel@vger.kernel.org, Zhuoyu.Zhang@freescale.com, Jason.Jin@freescale.com, linux-arm-kernel@lists.infradead.org, linux-pm@vger.kernel.org On Fri, Sep 26, 2014 at 9:20 PM, Mark Rutland <mark.rutland@arm.com> wrote: >> > This looks to be a carbon copy of the vexpress pseudo-hotplug in >> > arch/arm/mach-vexpress/hotplug.c, which is obviously broken in the way >> > you describe above. Perhaps we should go about ripping that out? >> >> The Versatile Express does not support suspend so the only problem case >> is kexec. However, isn't this support needed for big.LITTLE, and as >> the Versatile Express is the platform which these features get developed >> on, having working CPU hotplug seems rather fundamental for ARM kernel >> feature development. >> >> In that regard, Versatile Express is something of a special case. > > It is admittedly helpful during development to perform pseudo-hotplug on > Versatile Express. I have a local patch adding vexpress_cpu_disable so I > can test for bugs that only trigger if CPU0 is hotplugged. > > Given that, perhaps we should make it clearer that Versatile Express is > not a reference implementation for CPU hotplug; add some Kconfig (e.g. > VEXPRESS_PSEUDO_HOTPLUG) that depends on !KEXEC && !SUSPEND, and putting > a note in hotplug.c stating it's not suitable as a reference > implementation. > > ...but perhaps that's overkill. I agree that the pseudo-hotplug is breaking the kexec. However, I don't think it breaks the system suspend case as tasks and interrupts have been moved out of the non-booting CPU. The pseudo-hotplug would be even better than real hotplug as it introduces less latency. Regards, Leo ^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [PATCH 1/3] arm: ls1: add CPU hotplug platform support 2014-09-28 10:57 ` [PATCH 1/3] arm: ls1: add CPU hotplug platform support Li Yang @ 2014-09-28 14:27 ` Russell King - ARM Linux 0 siblings, 0 replies; 2+ messages in thread From: Russell King - ARM Linux @ 2014-09-28 14:27 UTC (permalink / raw) To: Li Yang Cc: Mark Rutland, Chenhui Zhao, kernel@pengutronix.de, linux-kernel@vger.kernel.org, Zhuoyu.Zhang@freescale.com, Jason.Jin@freescale.com, linux-arm-kernel@lists.infradead.org, linux-pm@vger.kernel.org On Sun, Sep 28, 2014 at 06:57:18PM +0800, Li Yang wrote: > On Fri, Sep 26, 2014 at 9:20 PM, Mark Rutland <mark.rutland@arm.com> wrote: > >> > This looks to be a carbon copy of the vexpress pseudo-hotplug in > >> > arch/arm/mach-vexpress/hotplug.c, which is obviously broken in the way > >> > you describe above. Perhaps we should go about ripping that out? > >> > >> The Versatile Express does not support suspend so the only problem case > >> is kexec. However, isn't this support needed for big.LITTLE, and as > >> the Versatile Express is the platform which these features get developed > >> on, having working CPU hotplug seems rather fundamental for ARM kernel > >> feature development. > >> > >> In that regard, Versatile Express is something of a special case. > > > > It is admittedly helpful during development to perform pseudo-hotplug on > > Versatile Express. I have a local patch adding vexpress_cpu_disable so I > > can test for bugs that only trigger if CPU0 is hotplugged. > > > > Given that, perhaps we should make it clearer that Versatile Express is > > not a reference implementation for CPU hotplug; add some Kconfig (e.g. > > VEXPRESS_PSEUDO_HOTPLUG) that depends on !KEXEC && !SUSPEND, and putting > > a note in hotplug.c stating it's not suitable as a reference > > implementation. > > > > ...but perhaps that's overkill. > > I agree that the pseudo-hotplug is breaking the kexec. However, I > don't think it breaks the system suspend case as tasks and interrupts > have been moved out of the non-booting CPU. The pseudo-hotplug would > be even better than real hotplug as it introduces less latency. Sorry, that's not an acceptable reason to use it. NAK. -- FTTC broadband for 0.8mile line: currently at 9.5Mbps down 400kbps up according to speedtest.net. ^ permalink raw reply [flat|nested] 2+ messages in thread
end of thread, other threads:[~2014-09-28 14:27 UTC | newest] Thread overview: 2+ messages (download: mbox.gz follow: Atom feed -- links below jump to the message on this page -- [not found] <1411730703-25836-1-git-send-email-chenhui.zhao@freescale.com> [not found] ` <1411730703-25836-2-git-send-email-chenhui.zhao@freescale.com> [not found] ` <20140926122003.GP5182@n2100.arm.linux.org.uk> [not found] ` <20140926124614.GD7422@leverpostej> [not found] ` <20140926130311.GQ5182@n2100.arm.linux.org.uk> [not found] ` <20140926132038.GF7422@leverpostej> 2014-09-28 10:57 ` [PATCH 1/3] arm: ls1: add CPU hotplug platform support Li Yang 2014-09-28 14:27 ` Russell King - ARM Linux
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