From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
To: Joe Buehler <aspam@cox.net>
Cc: kvm@vger.kernel.org
Subject: Re: probable vm exit latency issue?
Date: Fri, 15 Dec 2017 15:08:13 -0500 [thread overview]
Message-ID: <20171215200813.GB11465@char.us.oracle.com> (raw)
In-Reply-To: <5A342458.9010403@cox.net>
On Fri, Dec 15, 2017 at 02:36:56PM -0500, Joe Buehler wrote:
> I am debugging large latency issues in a realtime KVM instance, trying to make an existing VM (debugged on another type of box) run on an HP proliant now.
>
> cyclictest came up with the following snippet:
>
> kworker/-71 0.....11 13483223us : ata_sff_exec_command <-ata_bmdma_setup
> kworker/-71 0.....11 13483228us : ata_sff_sync <-ata_sff_exec_command
> kworker/-71 0.....11 13483231us : delay_tsc <-__const_udelay
> kworker/-71 0.....11 13483231us*: ata_bmdma_start <-ata_bmdma_qc_issue
> kworker/-71 0d....11 13496181us : smp_apic_timer_interrupt <-apic_timer_interrupt
> kworker/-71 0d....11 13496181us : irq_enter <-smp_apic_timer_interrupt
> kworker/-71 0d....11 13496182us : rcu_irq_enter <-irq_enter
>
> I don't have a lot of experience with this; is this a DMA start for disk I/O, presumably causing an exit from the VM? For almost 13 milliseconds????
>
> I haven't been able to find much obvious about eliminating this -- any suggestions? I set caching to writeback without effect.
>
> <disk type='file' device='disk'>
> <driver name='qemu' type='qcow2' cache='writeback'/>
> <source file='/boot.qcow2'/>
> <backingStore type='file' index='1'>
> <format type='raw'/>
> <source file='/root.qcow2'/>
> <backingStore/>
> </backingStore>
> <target dev='hdb' bus='ide'/>
> <alias name='ide0-0-1'/>
> <address type='drive' controller='0' bus='0' target='0' unit='1'/>
> </disk>
Um. Don't use IDE? Use VirtIO.
>
> Joe Buehler
next prev parent reply other threads:[~2017-12-15 20:08 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-12-15 19:36 probable vm exit latency issue? Joe Buehler
2017-12-15 20:08 ` Konrad Rzeszutek Wilk [this message]
[not found] ` <mL8E1w02Z1iuWrx01L8FMi>
2017-12-15 20:24 ` Joe Buehler
2017-12-15 20:48 ` Joe Buehler
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