From: Prarit Bhargava <prarit@redhat.com>
To: paulmck@linux.vnet.ibm.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: Fri, 12 Oct 2012 14:27:01 -0400 [thread overview]
Message-ID: <507860F5.7090908@redhat.com> (raw)
In-Reply-To: <20121011202103.GB2476@linux.vnet.ibm.com>
> 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.
P.
next prev parent reply other threads:[~2012-10-12 18:27 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 [this message]
2012-10-14 22:51 ` Paul E. McKenney
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