From: Marcelo Tosatti <mtosatti@redhat.com>
To: Zhanghailiang <zhang.zhanghailiang@huawei.com>
Cc: "johnstul@us.ibm.com" <johnstul@us.ibm.com>,
"tglx@linutronix.de" <tglx@linutronix.de>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Zhouxiangjiu <zhouxiangjiu@huawei.com>,
zhang yanying <zhuangyanying@huawei.com>
Subject: Re: VDSO pvclock may increase host cpu consumption, is this a problem?
Date: Sat, 29 Mar 2014 11:46:07 -0300 [thread overview]
Message-ID: <20140329144607.GA20316@amt.cnet> (raw)
In-Reply-To: <D1BD20B5DB34024DA951CEEE6C4C59985961AD4E@szxema505-mbs.china.huawei.com>
On Sat, Mar 29, 2014 at 08:47:27AM +0000, Zhanghailiang wrote:
> Hi,
> I found when Guest is idle, VDSO pvclock may increase host consumption.
> We can calcutate as follow, Correct me if I am wrong.
> (Host)250 * update_pvclock_gtod = 1500 * gettimeofday(Guest)
> In Host, VDSO pvclock introduce a notifier chain, pvclock_gtod_chain in timekeeping.c. It consume nearly 900 cycles per call. So in consideration of 250 Hz, it may consume 225,000 cycles per second, even no VM is created.
> In Guest, gettimeofday consumes 220 cycles per call with VDSO pvclock. If the no-kvmclock-vsyscall is configured, gettimeofday consumes 370 cycles per call. The feature decrease 150 cycles consumption per call.
> When call gettimeofday 1500 times,it decrease 225,000 cycles,equal to the host consumption.
> Both Host and Guest is linux-3.13.6.
> So, whether the host cpu consumption is a problem?
Hi,
How many percents out of the total CPU cycles are 225,000 cycles, for your
CPU ?
next prev parent reply other threads:[~2014-03-29 14:46 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-03-29 8:47 VDSO pvclock may increase host cpu consumption, is this a problem? Zhanghailiang
2014-03-29 14:46 ` Marcelo Tosatti [this message]
2014-03-31 1:12 ` Zhanghailiang
2014-03-31 17:52 ` Andy Lutomirski
2014-03-31 21:30 ` Marcelo Tosatti
2014-04-01 5:33 ` Andy Lutomirski
2014-04-01 18:01 ` Marcelo Tosatti
2014-04-01 19:17 ` Andy Lutomirski
2014-04-02 0:12 ` Marcelo Tosatti
2014-04-02 0:20 ` Andy Lutomirski
[not found] ` <20140402002926.GB31945@amt.cnet>
2014-04-02 0:46 ` Andy Lutomirski
2014-04-02 22:05 ` Marcelo Tosatti
2014-04-02 22:31 ` Andy Lutomirski
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