> The background to this is I've spent far too long trying to optimize > the conversion of qcow2 files to raw files. Most existing qcow2 files > that you can find online are zlib compressed, including the qcow2 > images provided by Fedora. Each cluster in the file is separately > compressed as a zlib stream, and qemu uses zlib library functions to > decompress them. When downloading and decompressing these files, I > measured 40%+ of the total CPU time is doing zlib decompression. > > [You don't need to tell me how great Zstd is, qcow2 supports this for > compression also, but it is not widely used by existing content.] Independent from the decision to use zlib-ng as a distro-wide zlib replacement, which is a good idea regardless. Are there reasons why Fedora's qcow2 images cannot switch to Zstd compression? Zstd support appears to have been added by QEMU 5.1 in August 2020, and both EL8 and EL9 appear to have newer versions QEMU available (therefore, they ought to be able to support those images). Sure, it doesn't help for existing content, but it would help for future content. And I'm pretty sure zstd remains faster than zlib-ng despite the speed improvements in the latter. _______________________________________________ devel mailing list -- devel@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe send an email to devel-leave@xxxxxxxxxxxxxxxxxxxxxxx Fedora Code of Conduct: https://docs.fedoraproject.org/en-US/project/code-of-conduct/ List Guidelines: https://fedoraproject.org/wiki/Mailing_list_guidelines List Archives: https://lists.fedoraproject.org/archives/list/devel@xxxxxxxxxxxxxxxxxxxxxxx Do not reply to spam, report it: https://pagure.io/fedora-infrastructure/new_issue
