AArch64: Backport memcpy improvements
Affects | Status | Importance | Assigned to | Milestone | |
---|---|---|---|---|---|
glibc (Ubuntu) |
Fix Released
|
Undecided
|
Unassigned | ||
Focal |
Fix Released
|
Undecided
|
Unassigned |
Bug Description
[impact]
glibc 2.32 contained a number of improvements to the memcpy routines for server-grade AArch64 implementations (in particular, graviton2 & graviton3). They should be backported to focal, as the LTS releases are by far the most used on servers.
[test case]
Download the "bench.tar.gz" attachment from this report. It has a README
that explains what to do, but here it is for reference:
benchmark for testing arm64 memcpy improvements in SRU
This is a benchmark that was derived from the memcpy benchmarks in glibc but altered to benchmark the public 'memcpy' symbol and be linked to the
installed libc.
To use this there are 5 steps:
1. build -- just run "make test"
2. run before upgrade -- "make bench-before"
3. upgrade libc6 package -- depends on what is being tested!
4. run again -- "make bench-after"
5. compare -- "make compare"
It produces output like this:
length | before (MiB/s) | after (MiB/s) | delta
-------
32768 | 233.74 | 248.03 | 6.11%
65536 | 443.72 | 468.69 | 5.63%
131072 | 853.71 | 895.08 | 4.84%
262144 | 1640.93 | 1718.91 | 4.75%
524288 | 2501.80 | 2604.83 | 4.12%
1048576 | 3896.77 | 4157.74 | 6.70%
On graviton2 systems, this should show an improvement of at least several percent. On other arm64 systems (raspberry pis of various vintage, thunderx2, xgene, etc etc) no significant regression should be seen.
[regression potential]
Rebuilding glibc is always a little risky (toolchain bugs and incompatibilities between the old and new versions can be surprising). But the autopkgtests and some manual general testing can help here.
For this specific change, there is a potential risk that the new memcpy implementation could be used on a system where it is not in fact the fastest. We should run the test case not only on the systems where it is expected to help, but other systems such as the RPi4 and the launchpad build farm to ensure performance is not regressed there.
Changed in glibc (Ubuntu): | |
status: | New → Invalid |
description: | updated |
Changed in glibc (Ubuntu Focal): | |
status: | New → In Progress |
description: | updated |
description: | updated |
Changed in glibc (Ubuntu): | |
status: | Invalid → Fix Released |
description: | updated |
description: | updated |
tags: |
added: verification-done-focal removed: verification-needed-focal |
tags: | removed: verification-needed |
Hello Michael, or anyone else affected,
Accepted glibc into focal-proposed. The package will build now and be available at https:/ /launchpad. net/ubuntu/ +source/ glibc/2. 31-0ubuntu9. 4 in a few hours, and then in the -proposed repository.
Please help us by testing this new package. See https:/ /wiki.ubuntu. com/Testing/ EnableProposed for documentation on how to enable and use -proposed. Your feedback will aid us getting this update out to other Ubuntu users.
If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested, what testing has been performed on the package and change the tag from verification- needed- focal to verification- done-focal. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification- failed- focal. In either case, without details of your testing we will not be able to proceed.
Further information regarding the verification process can be found at https:/ /wiki.ubuntu. com/QATeam/ PerformingSRUVe rification . Thank you in advance for helping!
N.B. The updated package will be released to -updates after the bug(s) fixed by this package have been verified and the package has been in -proposed for a minimum of 7 days.