Ubuntu
zfs-linux package

SIMD broken in 0.8.1 please backport fix, like Debian

Bug #1845018 reported by Garrett Fields
36
This bug affects 6 people
Affects Status Importance Assigned to Milestone
zfs-linux (Ubuntu)
Won't Fix
Medium
Colin Ian King

Bug Description

Eoan Ermine is using 0.8.1. On the current LiveCD, ZFS uses scalar instead of hardware accelerated SIMD instructions.

As of zfs-linux 0.8.1-3 (unstable) and 0.8.1-4~bpo10+1 (buster-backports), Debian has "Cherry-pick e5db313 to fix the linux-SIMD compatibility" (https://tracker.debian.org/news/1065134/accepted-zfs-linux-081-4bpo101-source-amd64-all-into-buster-backports-buster-backports/).

This fix will be included in 0.8.2, don't expect expect Eoan Ermine to move to that release.

Revision history for this message
Launchpad Janitor (janitor) wrote :

Status changed to 'Confirmed' because the bug affects multiple users.

Changed in zfs-linux (Ubuntu):
status: New → Confirmed
Revision history for this message
Garrett Fields (fields-g) wrote :

Just needed to add that this cherry-pick has been found to be a problem. Where it has been implemented, it has been retracted.

Issue: https://github.com/zfsonlinux/zfs/issues/9346
Issue: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=940932
Debian retraction 0.8.2-1 (unstable), also in 0.8.2-2 (backports) https://tracker.debian.org/news/1068877/accepted-zfs-linux-082-2bpo101-source-amd64-all-into-buster-backports/

Although, this certain cherry-pick shouldn't be used, this launchpad bug should remain open because the lack of SIMD functionality hurts ZFS performance. When a corrected fix is released, it should be considered for backport to 19.10.

Revision history for this message
Andreas Hasenack (ahasenack) wrote :

Yeah, on eoan I get:
$ cat /proc/spl/kstat/zfs/fletcher_4_bench
0 0 0x01 -1 0 4250112835 2191051355493
implementation native byteswap
scalar 7121128976 5682673600
superscalar 9132158207 6984205638
superscalar4 8279361738 6770847284
fastest superscalar superscalar

The same machine on bionic gets:
0 0 0x01 -1 0 67628130770 127422129063
implementation native byteswap
scalar 7105261516 5016484387
superscalar 9725496554 7224297957
superscalar4 8153749237 6904111964
sse2 16325929140 9147142980
ssse3 16010951957 14542922899
avx2 24379617040 23016231817
fastest avx2 avx2

Bionic's algorithm using avx2 is 2.6x faster.

Revision history for this message
Andreas Hasenack (ahasenack) wrote :

This is the PR to backport the master fix into 0.8.2:

https://github.com/zfsonlinux/zfs/pull/9515

Revision history for this message
Colin Ian King (colin-king) wrote :

Apologies for not getting around to fixing this. Eoan will be EOL next month, so I doubt I can get this fix into Eoan as SRU to benefit users before we hit EOL. Ubuntu Focal LTS has this support so I recommend upgrading to Focal.

Changed in zfs-linux (Ubuntu):
importance: Undecided → Medium
assignee: nobody → Colin Ian King (colin-king)
status: Confirmed → Won't Fix
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