Messages in this thread | | | Date | Tue, 21 Mar 2023 17:14:49 +0200 (EET) | From | Ilpo Järvinen <> | Subject | Re: [PATCH v3 08/19] x86/resctrl: Add cpumask_any_housekeeping() for limbo/overflow |
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On Mon, 20 Mar 2023, James Morse wrote:
> The limbo and overflow code picks a CPU to use from the domain's list > of online CPUs. Work is then scheduled on these CPUs to maintain > the limbo list and any counters that may overflow. > > cpumask_any() may pick a CPU that is marked nohz_full, which will > either penalise the work that CPU was dedicated to, or delay the > processing of limbo list or counters that may overflow. Perhaps > indefinitely. Delaying the overflow handling will skew the bandwidth > values calculated by mba_sc, which expects to be called once a second. > > Add cpumask_any_housekeeping() as a replacement for cpumask_any() > that prefers housekeeping CPUs. This helper will still return > a nohz_full CPU if that is the only option. The CPU to use is > re-evaluated each time the limbo/overflow work runs. This ensures > the work will move off a nohz_full CPU once a houskeeping CPU is
housekeeping
> available. > > Signed-off-by: James Morse <james.morse@arm.com> > --- > arch/x86/kernel/cpu/resctrl/internal.h | 23 +++++++++++++++++++++++ > arch/x86/kernel/cpu/resctrl/monitor.c | 17 ++++++++++++----- > include/linux/tick.h | 3 ++- > 3 files changed, 37 insertions(+), 6 deletions(-) > > diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h > index 87545e4beb70..0b5fd5a0cda2 100644 > --- a/arch/x86/kernel/cpu/resctrl/internal.h > +++ b/arch/x86/kernel/cpu/resctrl/internal.h > @@ -7,6 +7,7 @@ > #include <linux/kernfs.h> > #include <linux/fs_context.h> > #include <linux/jump_label.h> > +#include <linux/tick.h> > #include <asm/resctrl.h> > > #define L3_QOS_CDP_ENABLE 0x01ULL > @@ -55,6 +56,28 @@ > /* Max event bits supported */ > #define MAX_EVT_CONFIG_BITS GENMASK(6, 0) > > +/** > + * cpumask_any_housekeeping() - Chose any cpu in @mask, preferring those that > + * aren't marked nohz_full > + * @mask: The mask to pick a CPU from. > + * > + * Returns a CPU in @mask. If there are houskeeping CPUs that don't use > + * nohz_full, these are preferred. > + */ > +static inline unsigned int cpumask_any_housekeeping(const struct cpumask *mask) > +{ > + int cpu, hk_cpu; > + > + cpu = cpumask_any(mask); > + if (tick_nohz_full_cpu(cpu)) { > + hk_cpu = cpumask_nth_andnot(0, mask, tick_nohz_full_mask);
Why cpumask_nth_and() is not enough here? ..._andnot() seems to alter tick_nohz_full_mask which doesn't seem desirable?
-- i.
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