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RE: [ANNOUNCE] Xen 4.15 release schedule and feature tracking

  • To: "Cooper, Andrew" <andrew.cooper3@xxxxxxxxxx>, Ian Jackson <iwj@xxxxxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, "committers@xxxxxxxxxxxxxx" <committers@xxxxxxxxxxxxxx>, Tamas K Lengyel <tamas@xxxxxxxxxxxxx>, Michał Leszczyński <michal.leszczynski@xxxxxxx>
  • From: "Lengyel, Tamas" <tamas.lengyel@xxxxxxxxx>
  • Date: Fri, 15 Jan 2021 15:14:36 +0000
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  • Thread-topic: [ANNOUNCE] Xen 4.15 release schedule and feature tracking

> Features:
> 1) acquire_resource fixes.
> Not really a new feature - entirely bugfixing a preexisting one.
> Developed by me to help 2).  Reasonably well acked, but awaiting feedback
> on v3.
> 2) External Processor Trace support.
> Development by Michał.  Depends on 1), and awaiting a new version being
> posted.
> As far as I'm aware, both Intel and CERT have production systems deployed
> using this functionality, so it is very highly desirable to get into 4.15.

We are actively using a backported version on top of 4.14.1, having this in 
4.15 would be absolutely huge. We've ran over 10 billion fuzz cycles using it 
so far using VM forks, works great. Several other researchers in the community 
are using it as well.

> 1) HPET/PIT issue on newer Intel systems.  This has had literally tens of
> reports across the devel and users mailing lists, and prevents Xen from
> booting at all on the past two generations of Intel laptop.  I've finally got 
> a
> repro and posted a fix to the list, but still in progress.

We've ran into this on multiple systems, Andrew's patch does fix it.

> 2) "scheduler broken" bugs.  We've had 4 or 5 reports of Xen not working,
> and very little investigation on whats going on.  Suspicion is that there
> might be two bugs, one with smt=0 on recent AMD hardware, and one
> more general "some workloads cause negative credit" and might or might
> not be specific to credit2 (debugging feedback differs - also might be 3
> underlying issue).

We've also ran into intermittent Xen lockups requiring power-cycling servers. 
We switched back to credit1 and had no issues since. Hard to tell if it was 
related to the scheduler or the pile of other experimental stuff we are running 
with but right now we have stable systems across the board with credit1.

> All of these have had repeated bug reports.  I'd classify them as blockers,
> given the impact they're having on people.





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