[OASIS Issue Tracker] (VIRTIO-144) VIRTIO_BLK_F_CONFIG_WCE removed from block devices spec

[OASIS Issues Tracker <workgroup_mailer@lists.oasis-open.org>]

     [ https://issues.oasis-open.org/browse/VIRTIO-144?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Michael S. Tsirkin updated VIRTIO-144:
--------------------------------------

    Proposal: 
Clarify definition of writeback and writethrough caching, clarify the influence of the
VIRTIO_BLK_F_FLUSH feature on caching, strengthen the requirement for persisting writes to MUST after a VIRTIO_BLK_T_FLUSH request (and in other cases too involving the new features), introduce VIRTIO_BLK_F_FLUSH and VIRTIO_BLK_F_CONFIG_WCE for non-transitional devices.
https://lists.oasis-open.org/archives/virtio/201508/msg00024.html

  was:
Clarify definition of writeback and writethrough caching, clarify the influence of the
VIRTIO_BLK_F_FLUSH feature on caching, strengthen the requirement for persisting writes to MUST after a VIRTIO_BLK_T_FLUSH request (and in other cases too involving the new features), introduce VIRTIO_BLK_F_FLUSH and VIRTIO_BLK_F_CONFIG_WCE for non-transitional devices.

https://lists.oasis-open.org/archives/virtio/201507/msg00007.html
https://lists.oasis-open.org/archives/virtio/201507/msg00030.html
https://lists.oasis-open.org/archives/virtio/201507/msg00049.html


> VIRTIO_BLK_F_CONFIG_WCE removed from block devices spec
> -------------------------------------------------------
>
>                 Key: VIRTIO-144
>                 URL: https://issues.oasis-open.org/browse/VIRTIO-144
>             Project: OASIS Virtual I/O Device (VIRTIO) TC
>          Issue Type: Bug
>    Affects Versions: virtio 1.0 cs03
>         Environment: Paolo Bonzini <pbonzini@redhat.com>
>            Reporter: Paolo Bonzini
>            Assignee: Paolo Bonzini
>            Priority: Critical
>              Labels: AdoptionBlocker
>             Fix For: virtio 1.0 cs04
>
>
> VIRTIO_BLK_F_CONFIG_WCE is important in order to achieve good performance (up to 2x, though more realistically +30-40%) in latency-bound workloads. However, it was removed by mistake together with VIRTIO_BLK_F_FLUSH.
> The lack of this feature means that virtio 1.0 cs02 does not achieve parity with 0.9.



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