On Mon, Apr 26, 2021 at 3:31 AM Chris Murphy <lists@xxxxxxxxxxxxxxxxx> wrote:
On Sun, Apr 25, 2021 at 12:39 PM Artem Tim <ego.cordatus@xxxxxxxxx> wrote:
> Upcoming 5.12 allow building with dynamic preemption support which allows changing mode at boot/run-time so finally no need to rebuild or make alternative kernel build anymore[1]. Responsive system is a must have for gaming and good desktop experience overall, not only for professional audio. For example difference in input mouse lag is like day and night with PREEMPT mode. Maybe on cheap mouse this is hard to notice but on 500-1000Hz mouse really easy. You can test this yourself with experimental kernel build on COPR[2]. Some Linux distros[3] already using PREEMPT mode by default for a decent period of time. Fedora kernel build with CONFIG_PREEMPT_VOLUNTARY but this is not enough for desktop use case.
>
> Please provide full PREEMPT mode by default in 5.12 kernel for desktop variants. With 5.12 it is possible for user to change it without efforts if they need this.
>
I see CONFIG_HAVE_PREEMPT_DYNAMIC=y with kernel
5.12.0-0.rc8.191.fc35.x86_64+debug.
CONFIG_HAVE_PREEMPT_DYNAMIC only says the architecture supports the feature. This is hard-coded by arch/x86/Kconfig.
To actually enable the feature, CONFIG_PREEMPT=y would have to be set. The combination of CONFIG_PREEMPT and CONFIG_HAVE_PREEMPT_DYNAMIC then selects CONFIG_PREEMPT_DYNAMIC. See kernel/Kconfig.preempt.
Michal
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