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 an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.