From: Stefan Hajnoczi <stefanha@gmail.com>
To: 浩樊啊 <fanh2010@foxmail.com>
Cc: qemu-devel <qemu-devel@nongnu.org>
Subject: Re: [Qemu-devel] about I/O
Date: Thu, 7 Jan 2016 13:05:25 +0800 [thread overview]
Message-ID: <20160107050525.GD12971@stefanha-x1.localdomain> (raw)
In-Reply-To: <tencent_188DEB20579AFDDF2C219C1E@qq.com>
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On Tue, Dec 29, 2015 at 03:36:07PM +0800, 浩樊啊 wrote:
> qemu use paio or libaio finish I/O reqeusts,does that mean that when a sync request comes from a vm becomes async request in the host?
Yes, although storage controllers (virtio-blk, SCSI, SATA, and even IDE
in DMA mode) are asynchronous at the hardware interface level. That
means the guest OS submits an I/O request to the device and the guest
CPU continues running until the I/O completion interrupt occurs.
The exceptions are old hardware interfaces like some of the SD Card
controllers or maybe floppy where a single hardware register read/write
actually involves synchronous I/O (the guest cannot execute CPU
instructions while the I/O request is happening).
Stefan
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parent reply other threads:[~2016-01-07 5:05 UTC|newest]
Thread overview: expand[flat|nested] mbox.gz Atom feed
[parent not found: <tencent_188DEB20579AFDDF2C219C1E@qq.com>]
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