linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
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.

  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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20191120150016.GA3383@lenoir \
    --to=frederic@kernel.org \
    --cc=benh@kernel.crashing.org \
    --cc=jacek.anaszewski@gmail.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mingo@kernel.org \
    --cc=pavel@ucw.cz \
    --cc=peterz@infradead.org \
    --cc=riel@surriel.com \
    --cc=rjw@rjwysocki.net \
    --cc=tglx@linutronix.de \
    --cc=viresh.kumar@linaro.org \
    --cc=wanpengli@tencent.com \
    --cc=yauheni.kaliuta@redhat.com \
    --subject='Re: [PATCH 2/6] sched/vtime: Bring all-in-one kcpustat accessor for vtime fields' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).