From: Frederic Weisbecker <frederic@kernel.org>
To: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
LKML <linux-kernel@vger.kernel.org>,
Jacek Anaszewski <jacek.anaszewski@gmail.com>,
Wanpeng Li <wanpengli@tencent.com>,
"Rafael J . Wysocki" <rjw@rjwysocki.net>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Rik van Riel <riel@surriel.com>,
Thomas Gleixner <tglx@linutronix.de>,
Yauheni Kaliuta <yauheni.kaliuta@redhat.com>,
Viresh Kumar <viresh.kumar@linaro.org>,
Pavel Machek <pavel@ucw.cz>
Subject: Re: [PATCH 2/6] sched/vtime: Bring all-in-one kcpustat accessor for vtime fields
Date: Wed, 20 Nov 2019 16:00:17 +0100 [thread overview]
Message-ID: <20191120150016.GA3383@lenoir> (raw)
In-Reply-To: <20191120120449.GB89662@gmail.com>
On Wed, Nov 20, 2019 at 01:04:49PM +0100, Ingo Molnar wrote:
> > +static int vtime_state_check(struct vtime *vtime, int cpu)
> > +{
> > + /*
> > + * We raced against context switch, fetch the
> > + * kcpustat task again.
> > + */
>
> s/against context switch
> /against a context switch
Ok.
>
> > +void kcpustat_cputime(struct kernel_cpustat *kcpustat, int cpu,
> > + u64 *user, u64 *nice, u64 *system,
> > + u64 *guest, u64 *guest_nice)
> > +{
> > + u64 *cpustat = kcpustat->cpustat;
> > + struct rq *rq;
> > + int err;
> > +
> > + if (!vtime_accounting_enabled_cpu(cpu)) {
> > + kcpustat_cputime_raw(cpustat, user, nice,
> > + system, guest, guest_nice);
> > + return;
> > + }
> > +
> > + rq = cpu_rq(cpu);
> > +
> > + for (;;) {
> > + struct task_struct *curr;
> > +
> > + rcu_read_lock();
> > + curr = rcu_dereference(rq->curr);
> > + if (WARN_ON_ONCE(!curr)) {
> > + rcu_read_unlock();
> > + kcpustat_cputime_raw(cpustat, user, nice,
> > + system, guest, guest_nice);
> > + return;
> > + }
> > +
> > + err = kcpustat_cputime_vtime(cpustat, curr, cpu, user,
> > + nice, system, guest, guest_nice);
> > + rcu_read_unlock();
> > +
> > + if (!err)
> > + return;
> > +
> > + cpu_relax();
> > + }
> > +}
> > +EXPORT_SYMBOL_GPL(kcpustat_cputime);
>
> I'm wondering whether it's worth introducing a helper structure for this
> train of parameters: user, nice, system, guest, guest_nice?
>
> We also have similar constructs in other places:
>
> + u64 cpu_user, cpu_nice, cpu_sys, cpu_guest, cpu_guest_nice;
>
> But more broadly, what do we gain by passing along a quartet of pointers,
> while we could also just use a 'struct kernel_cpustat' and store the
> values there naturally?
>
> Yes, it's larger, because it also has 5 other fields - but we lose much
> of the space savings due to always passing along the 4 pointers already.
>
> So I really think the parameter passing should be organized better here.
Yeah I've been thinking about that too but I was worried about the stack use.
It's probably not a big worry eventually. I'll do that for the next series.
> This probably affects similar cpustat functions as well.
Only this one fortunately :-)
Thanks.
next prev parent reply other threads:[~2019-11-20 15:00 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-19 23:22 [PATCH 0/6] sched/nohz: Make the rest of kcpustat vtime aware v2 Frederic Weisbecker
2019-11-19 23:22 ` [PATCH 1/6] sched/cputime: Support other fields on kcpustat_field() Frederic Weisbecker
2019-11-20 11:51 ` Ingo Molnar
2019-11-20 21:04 ` Peter Zijlstra
2019-11-19 23:22 ` [PATCH 2/6] sched/vtime: Bring all-in-one kcpustat accessor for vtime fields Frederic Weisbecker
2019-11-20 12:04 ` Ingo Molnar
2019-11-20 15:00 ` Frederic Weisbecker [this message]
2019-11-19 23:22 ` [PATCH 3/6] procfs: Use all-in-one vtime aware kcpustat accessor Frederic Weisbecker
2019-11-19 23:22 ` [PATCH 4/6] cpufreq: Use vtime aware kcpustat accessors for user time Frederic Weisbecker
2019-11-19 23:22 ` [PATCH 5/6] leds: Use all-in-one vtime aware kcpustat accessor Frederic Weisbecker
2019-11-19 23:22 ` [PATCH 6/6] rackmeter: Use " Frederic Weisbecker
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