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Date: Mon, 13 Jul 2020 14:55:43 +0200 From: Peter Zijlstra <peterz@...radead.org> To: Valentin Schneider <valentin.schneider@....com> Cc: linux-kernel@...r.kernel.org, mingo@...nel.org, vincent.guittot@...aro.org, dietmar.eggemann@....com, morten.rasmussen@....com Subject: Re: [PATCH v3 7/7] sched/topology: Use prebuilt SD flag degeneration mask On Wed, Jul 01, 2020 at 08:06:55PM +0100, Valentin Schneider wrote: > Leverage SD_DEGENERATE_GROUPS_MASK in sd_degenerate() and > sd_degenerate_parent(). > > Note that this changes sd_degenerate() somewhat: I'm using the negation of > SD_DEGENERATE_GROUPS_MASK as the mask of flags not requiring groups, which > is equivalent to: > > SD_WAKE_AFFINE | SD_SERIALIZE | SD_NUMA > > whereas the current mask for that is simply > > SD_WAKE_AFFINE > > I played with a few toy NUMA topologies on QEMU and couldn't cause a > different degeneration than what mainline does currently. If that is deemed > too risky, we can go back to using SD_WAKE_AFFINE explicitly. Arguably SD_SERIALIZE needs groups, note how we're only having that effective for machines with at least 2 nodes. It's a bit shit how we end up there, but IIRC that's what it ends up as. SD_NUMA is descriptive, and not marking a group as degenerates because it has SD_NUMA seems a bit silly. But then, it would be the top domain and would survive anyway?
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