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Date: Mon, 13 Apr 2015 20:49:20 -0400 From: Chris Metcalf <cmetcalf@...hip.com> To: Frederic Weisbecker <fweisbec@...il.com> CC: "Peter Zijlstra (Intel)" <peterz@...radead.org>, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>, "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>, Martin Schwidefsky <schwidefsky@...ibm.com>, Ingo Molnar <mingo@...hat.com>, <linux-kernel@...r.kernel.org> Subject: Re: [PATCH v7 1/2] nohz: add tick_nohz_full_add_cpus_to() and _remove_cpus_from() APIs On 4/13/2015 8:33 PM, Frederic Weisbecker wrote: > On Fri, Apr 10, 2015 at 04:53:51PM -0400, Chris Metcalf wrote: >> The "removes_cpus_from" API is useful, for example, to modify a cpumask >> to avoid the nohz cores so that interrupts aren't sent to them. >> >> Likewise the "add_cpus_to" API is useful to modify a cpumask indicating >> some special nohz-type functionality so that the nohz cores are >> automatically added to that set. >> >> Signed-off-by: Chris Metcalf <cmetcalf@...hip.com> >> --- >> [...] >> >> diff --git a/include/linux/tick.h b/include/linux/tick.h >> index 9c085dc12ae9..8d1754c0f694 100644 >> --- a/include/linux/tick.h >> +++ b/include/linux/tick.h >> @@ -186,6 +186,18 @@ static inline bool tick_nohz_full_cpu(int cpu) >> return cpumask_test_cpu(cpu, tick_nohz_full_mask); >> } >> >> +static inline void tick_nohz_full_add_cpus_to(struct cpumask *mask) >> +{ >> + if (tick_nohz_full_enabled()) >> + cpumask_or(mask, mask, tick_nohz_full_mask); >> +} >> + >> +static inline void tick_nohz_full_remove_cpus_from(struct cpumask *mask) >> +{ >> + if (tick_nohz_full_enabled()) >> + cpumask_andnot(mask, mask, tick_nohz_full_mask); > I would prefer that you don't introduce new APIs if they aren't used in your > patchset. It seems that's the case for tick_nohz_full_remove_cpus_from(). Yes, it's used in a tile-tree patch to remove nohz_full cpus from the set that take interrupts from the tilegx network driver. I can certainly make this patchset have just the _add_cpus_to() variant, and the other patchset have just the _remove_cpus_from() variant. It seemed to make sense to include them together as a matched set, but doing it the way you suggest makes an equal if different amount of sense. > Also we have housekeeping_affine() that affines a task to CPUs outside the > range of nohz full. In case you still need tick_nohz_full_remove_cpus_from() > in a further patchset, housekeeping_affine_cpumask() would extend the existing > naming. I like housekeeping_affine(), but it overwrites the affinity mask of the task. So I would expect housekeeping_affine_mask() to overwrite the specified argument cpumask, which it doesn't in my definition. I don't know that I can think of a good name in the "housekeeping_xxx" namespace that feels better than the one I proposed. In context of the proposed client of the API so far, it's: if (!network_cpus_init()) { network_cpus_map = *cpu_online_mask; tick_nohz_full_remove_cpus_from(&network_cpus_map); } If housekeeping_mask were defined for non-nohz_full I could just use it unconditionally here. Alternately I could just put in an #ifdef for CONFIG_NO_HZ_FULL and either use cpu_only_mask or housekeeping_mask to initialize network_cpus_map, which dodges the bullet of creating an acceptable API name here for the moment. Frederic, what's your thought/preference? -- Chris Metcalf, EZChip Semiconductor http://www.ezchip.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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