On 01.11.19 13:40, Eric Blake wrote: > On 11/1/19 11:00 AM, Max Reitz wrote: >> This reverts commit c8bb23cbdbe32f5c326365e0a82e1b0e68cdcd8a. >> >> This commit causes fundamental performance problems on XFS (because >> fallocate() stalls the AIO pipeline), and as such it is not clear that >> we should unconditionally enable this behavior. >> >> We expect subclusters to alleviate the performance penalty of small >> writes to newly allocated clusters, so when we get them, the originally >> intended performance gain may actually no longer be significant. >> >> If we want to reintroduce something similar to c8bb23cbdbe, it will >> require extensive benchmarking on various systems with subclusters >> enabled. >> >> Cc: qemu-sta...@nongnu.org >> Signed-off-by: Max Reitz <mre...@redhat.com> >> --- > >> +++ b/qapi/block-core.json >> @@ -3304,8 +3304,6 @@ >> # >> # @cor_write: a write due to copy-on-read (since 2.11) >> # >> -# @cluster_alloc_space: an allocation of file space for a cluster >> (since 4.1) >> -# >> # @none: triggers once at creation of the blkdebug node (since 4.1) > > Deleting released qapi is not backwards-compatible.
Right. :-/ I’ll just not make changes to the QAPI schema. It doesn’t hurt to leave this in. Max > However, given that > the only known user of this interface is debug testing via iotests, I'm > not too concerned that we would be impacting any external users.
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