From: Mike Galbraith <umgwanakikbuti@gmail.com>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Rik van Riel <riel@redhat.com>,
linux-kernel@vger.kernel.org, tglx@linutronix.de,
mingo@kernel.org, peterz@infradead.org, luto@amacapital.net,
Clark Williams <williams@redhat.com>
Subject: Re: [PATCH 2/2] sched,time: call __acct_update_integrals once a jiffy
Date: Sun, 31 Jan 2016 03:52:25 +0100 [thread overview]
Message-ID: <1454208745.3688.14.camel@gmail.com> (raw)
In-Reply-To: <20160130203602.GA7856@lerouge>
On Sat, 2016-01-30 at 21:36 +0100, Frederic Weisbecker wrote:
> On Sat, Jan 30, 2016 at 06:53:05PM +0100, Mike Galbraith wrote:
> > On Sat, 2016-01-30 at 15:20 +0100, Frederic Weisbecker wrote:
> > > On Fri, Jan 29, 2016 at 05:43:28PM -0500, Rik van Riel wrote:
> >
> > > > Run times for the microbenchmark:
> > > >
> > > > 4.4 3.8 seconds
> > > > 4.5-rc1 3.7 seconds
> > > > 4.5-rc1 + first patch 3.3 seconds
> > > > 4.5-rc1 + both patches 2.3 seconds
> > >
> > > Very nice improvement!
> >
> > Tasty indeed.
> >
> > When nohz_full CPUs are not isolated, ie are being used as generic
> > CPUs, get_nohz_timer_target() is a problem with things like tbench.
>
> So by isolated CPU you mean those part of isolcpus= boot option,
> right?
Yes, isolated in the scheduler sense, either via isolcpus= or cpusets.
If the CPU is part of a scheduler domain, it is by definition part of
the generic work crew.
> > tbench 8 with Rik's patches applied:
> > nohz_full=empty
> > Throughput 3204.69 MB/sec 1.000
> > nohz_full=1-3,5-7
> > Throughput 1354.99 MB/sec .422 1.000
> > nohz_full=1-3,5-7 + club below
> > Throughput 2762.22 MB/sec .861 2.038
> >
> > With Rik's patches and a club, tbench becomes nearly acceptable.
> > ---
> > include/linux/tick.h | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > --- a/include/linux/tick.h
> > +++ b/include/linux/tick.h
> > @@ -184,7 +184,7 @@ static inline const struct cpumask *hous
> > static inline bool is_housekeeping_cpu(int cpu)
> > {
> > #ifdef CONFIG_NO_HZ_FULL
> > - if (tick_nohz_full_enabled())
> > + if (tick_nohz_full_enabled() && runqueue_is_isolated(cpu))
> > return cpumask_test_cpu(cpu, housekeeping_mask);
>
> This makes me confused. How forcing timers to CPUs in isolcpus is making
> better results?
It doesn't, it's shutting get_nohz_timer_target() down for those
nohz_full CPUs that are NOT currently isolated, are thus generic CPUs
with the capability to _become_ elite solo artists on demand.
-Mike
next prev parent reply other threads:[~2016-01-31 2:52 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-29 22:22 [PATCH 0/2] sched,time: reduce nohz_full syscall overhead 40% riel
2016-01-29 22:22 ` [PATCH 1/2] sched,time: remove pointless divides from __acct_update_integrals riel
2016-01-29 23:10 ` Peter Zijlstra
2016-01-30 3:36 ` Frederic Weisbecker
2016-01-30 3:47 ` Rik van Riel
2016-01-29 22:23 ` [PATCH 2/2] sched,time: call __acct_update_integrals once a jiffy riel
2016-01-29 22:43 ` Rik van Riel
2016-01-30 14:20 ` Frederic Weisbecker
2016-01-30 17:53 ` Mike Galbraith
2016-01-30 20:36 ` Frederic Weisbecker
2016-01-31 2:52 ` Mike Galbraith [this message]
2016-01-31 5:37 ` Mike Galbraith
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=1454208745.3688.14.camel@gmail.com \
--to=umgwanakikbuti@gmail.com \
--cc=fweisbec@gmail.com \
--cc=linux-kernel@vger.kernel.org \
--cc=luto@amacapital.net \
--cc=mingo@kernel.org \
--cc=peterz@infradead.org \
--cc=riel@redhat.com \
--cc=tglx@linutronix.de \
--cc=williams@redhat.com \
/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
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
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).