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From: Joe Buehler <aspam@cox.net>
To: unlisted-recipients:; (no To-header on input)
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>, kvm@vger.kernel.org
Subject: Re: probable vm exit latency issue?
Date: Fri, 15 Dec 2017 15:48:02 -0500	[thread overview]
Message-ID: <5A343502.8060901@cox.net> (raw)
In-Reply-To: <5A342F85.9070406@cox.net>

I switched back to virtio for the disk; it has the same issue.  It apparently exits the VM via vp_notify(); in the trace I am looking at for almost 8 milliseconds.

I had been thinking in terms of disk writes but of course this could be any disk activity so overlayroot will not solve this.  It would seem that I might be looking at an inevitable disk rotation latency, which no host tuning will fix.

Would a second CPU in the VM solve this or does virtio halt the whole VM for disk I/O?

Or perhaps what I really need is to quiesce everything else in the VM to avoid all disk I/O?  I suppose I could use a RAM root filesystem -- ugh.

I find it a little puzzling that I have not seen disk I/O mentioned much in the realtime KVM literature I have found on the web.

Joe Buehler

      reply	other threads:[~2017-12-15 20:48 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
     [not found] ` <mL8E1w02Z1iuWrx01L8FMi>
2017-12-15 20:24   ` Joe Buehler
2017-12-15 20:48     ` Joe Buehler [this message]

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