From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Prarit Bhargava <prarit@redhat.com>
Cc: John Stultz <johnstul@us.ibm.com>,
Linux Kernel <linux-kernel@vger.kernel.org>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: RCU NOHZ, tsc, and clock_gettime
Date: Sun, 14 Oct 2012 15:51:35 -0700 [thread overview]
Message-ID: <20121014225135.GA3288@linux.vnet.ibm.com> (raw)
In-Reply-To: <507860F5.7090908@redhat.com>
On Fri, Oct 12, 2012 at 02:27:01PM -0400, Prarit Bhargava wrote:
>
> > The effect of removing the two functions you noted (on 3.6 and earlier)
> > is to prevent RCU from checking for dyntick-idle CPUs, likely incurring
> > a cache miss for each CPU with interrupts disabled. If you have a lot
> > of CPUs (or even if NR_CPUS is large and you have a smaller number of
> > CPUs), this can result in user-space-visible delays.
> >
>
> Paul,
>
> I built a kernel with NR_CPUS=48 and booted on a 48 cpu (logical) system. I do
> not see a difference in the test -- the variance is AFAICT just as large as if I
> had run with NR_CPUS=4096.
OK -- have you applied John Stultz's suggestions?
Thanx, Paul
prev parent reply other threads:[~2012-10-14 22:51 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-10-11 18:52 RCU NOHZ, tsc, and clock_gettime Prarit Bhargava
2012-10-11 19:51 ` John Stultz
2012-10-11 20:21 ` Paul E. McKenney
2012-10-12 15:40 ` Prarit Bhargava
2012-10-15 14:56 ` Paul E. McKenney
2012-11-12 23:27 ` John Stultz
2012-11-13 15:18 ` Prarit Bhargava
2012-10-12 18:27 ` Prarit Bhargava
2012-10-14 22:51 ` Paul E. McKenney [this message]
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=20121014225135.GA3288@linux.vnet.ibm.com \
--to=paulmck@linux.vnet.ibm.com \
--cc=johnstul@us.ibm.com \
--cc=linux-kernel@vger.kernel.org \
--cc=prarit@redhat.com \
--cc=tglx@linutronix.de \
/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