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Re: [Qemu-devel] The WCE issue in guest when i enable WCE in Qemu side.
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From: |
Paolo Bonzini |
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Subject: |
Re: [Qemu-devel] The WCE issue in guest when i enable WCE in Qemu side. |
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Date: |
Wed, 24 Jul 2019 10:57:30 +0200 |
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User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 |
On 24/07/19 08:55, Yang Zhong wrote:
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> The SPDK code i am using is latest version, So, i feel we should
> enable WCE feature in SPDK side by default. thanks for your help!
Note that enabling the CONFIG_WCE feature has some consequences.
According to the spec:
- if the VIRTIO_BLK_F_CONFIG_WCE feature was negotiated and the
writeback field in configuration space was 0 all the time between the
submission of the write and its completion, the device MUST ensure that
stable writes are committed to persistent storage before reporting
completion of the write. This means using FUA writes or something like that
- the device MUST offset VIRTIO_BLK_F_FLUSH if they offer
VIRTIO_BLK_F_CONFIG_WCE
- if VIRTIO_BLK_F_CONFIG_WCE is negotiated but VIRTIO_BLK_F_FLUSH is
not, the device MUST initialize writeback to 0
Paolo