From: Johannes Weiner <hannes@cmpxchg.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Tejun Heo <tj@kernel.org>, Suren Baghdasaryan <surenb@google.com>,
Daniel Drake <drake@endlessm.com>,
Vinayak Menon <vinmenon@codeaurora.org>,
Christopher Lameter <cl@linux.com>,
Mike Galbraith <efault@gmx.de>,
Shakeel Butt <shakeelb@google.com>,
Peter Enderborg <peter.enderborg@sony.com>,
linux-mm@kvack.org, cgroups@vger.kernel.org,
linux-kernel@vger.kernel.org, kernel-team@fb.com
Subject: Re: [PATCH 8/9] psi: pressure stall information for CPU, memory, and IO
Date: Mon, 6 Aug 2018 11:23:54 -0400 [thread overview]
Message-ID: <20180806152354.GC9888@cmpxchg.org> (raw)
In-Reply-To: <20180803170733.GC2494@hirez.programming.kicks-ass.net>
On Fri, Aug 03, 2018 at 07:07:33PM +0200, Peter Zijlstra wrote:
> On Wed, Aug 01, 2018 at 11:19:57AM -0400, Johannes Weiner wrote:
> > +static bool psi_update_stats(struct psi_group *group)
> > +{
> > + u64 deltas[NR_PSI_STATES - 1] = { 0, };
> > + unsigned long missed_periods = 0;
> > + unsigned long nonidle_total = 0;
> > + u64 now, expires, period;
> > + int cpu;
> > + int s;
> > +
> > + mutex_lock(&group->stat_lock);
> > +
> > + /*
> > + * Collect the per-cpu time buckets and average them into a
> > + * single time sample that is normalized to wallclock time.
> > + *
> > + * For averaging, each CPU is weighted by its non-idle time in
> > + * the sampling period. This eliminates artifacts from uneven
> > + * loading, or even entirely idle CPUs.
> > + *
> > + * We don't need to synchronize against CPU hotplugging. If we
> > + * see a CPU that's online and has samples, we incorporate it.
> > + */
> > + for_each_online_cpu(cpu) {
>
> I'm still puzzled by this.. for 99% of the machines online == possible.
> Why not always iterate possible and leave it at that? This is hardly a
> fast path.
Hmm, you're right, that makes things much simpler. I guess I'm mostly
worried about the 1% where this significantly differs, but it looks
like we're smarter than simply doing CONFIG_NR_CPUS for the possible
map, and we can easily stomach a bit of discrepancy in this path.
I'll change that to possible and delete/update the third paragraph.
Thanks
next prev parent reply other threads:[~2018-08-06 15:21 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20180801151958.32590-1-hannes@cmpxchg.org>
2018-08-01 15:19 ` [PATCH 1/9] mm: workingset: don't drop refault information prematurely Johannes Weiner
2018-08-01 15:19 ` [PATCH 2/9] mm: workingset: tell cache transitions from workingset thrashing Johannes Weiner
[not found] ` <CAJuCfpGZGPD+k+jHDowWyvZPnUXzQ9n98wBycDZLAWOn=vV6Ew@mail.gmail.com>
2018-08-02 12:28 ` Johannes Weiner
2018-08-01 15:19 ` [PATCH 3/9] delayacct: track delays from thrashing cache pages Johannes Weiner
2018-08-01 15:19 ` [PATCH 4/9] sched: loadavg: consolidate LOAD_INT, LOAD_FRAC, CALC_LOAD Johannes Weiner
2018-08-01 15:19 ` [PATCH 5/9] sched: loadavg: make calc_load_n() public Johannes Weiner
2018-08-01 15:19 ` [PATCH 6/9] sched: sched.h: make rq locking and clock functions available in stats.h Johannes Weiner
2018-08-01 15:19 ` [PATCH 7/9] sched: introduce this_rq_lock_irq() Johannes Weiner
2018-08-01 15:19 ` [PATCH 8/9] psi: pressure stall information for CPU, memory, and IO Johannes Weiner
2018-08-03 16:56 ` Peter Zijlstra
2018-08-06 15:05 ` Johannes Weiner
2018-08-06 15:25 ` Peter Zijlstra
2018-08-06 15:40 ` Johannes Weiner
2018-08-06 15:19 ` Johannes Weiner
2018-08-06 16:03 ` Peter Zijlstra
2018-08-21 19:44 ` Johannes Weiner
2018-08-22 9:16 ` Peter Zijlstra
2018-08-03 17:07 ` Peter Zijlstra
2018-08-06 15:23 ` Johannes Weiner [this message]
2018-08-03 17:15 ` Peter Zijlstra
2018-08-03 17:21 ` Peter Zijlstra
2018-08-21 20:11 ` Johannes Weiner
2018-08-22 9:10 ` Peter Zijlstra
2018-08-22 17:28 ` Johannes Weiner
2018-08-01 15:19 ` [PATCH 9/9] psi: cgroup support Johannes Weiner
2018-08-07 11:50 ` [PATCH 0/9] psi: pressure stall information for CPU, memory, and IO v3 peter enderborg
2018-08-07 17:51 ` Johannes Weiner
2018-08-28 17:22 [PATCH 0/9] psi: pressure stall information for CPU, memory, and IO v4 Johannes Weiner
2018-08-28 17:22 ` [PATCH 8/9] psi: pressure stall information for CPU, memory, and IO Johannes Weiner
2018-08-28 20:11 ` Randy Dunlap
2018-08-28 20:56 ` Johannes Weiner
2018-08-28 21:30 ` Randy Dunlap
2018-09-07 10:16 ` Peter Zijlstra
2018-09-07 10:21 ` Peter Zijlstra
2018-09-07 14:44 ` Johannes Weiner
2018-09-07 14:58 ` Peter Zijlstra
2018-09-07 17:50 ` Johannes Weiner
2018-09-07 10:24 ` Peter Zijlstra
2018-09-07 14:54 ` Johannes Weiner
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