Re: [Xen-devel] [PATCH v2 0/4] xen/rcu: let rcu work better with core scheduling

[Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>]

On 18/02/2020 12:21, Juergen Gross wrote:
> Today the RCU handling in Xen is affecting scheduling in several ways.
> It is raising sched softirqs without any real need and it requires
> tasklets for rcu_barrier(), which interacts badly with core scheduling.
> 
> This small series repairs those issues.
> 
> Additionally some ASSERT()s are added for verification of sane rcu
> handling. In order to avoid those triggering right away the obvious
> violations are fixed.

I've done more testing of this with [1] and, unfortunately, it quite easily
deadlocks while without this series it doesn't.

Steps to repro:
- apply [1]
- take a host with considerable CPU count (~64)
- run a loop: xen-hptool smt-disable; xen-hptool smt-enable

[1] https://lists.xenproject.org/archives/html/xen-devel/2020-02/msg01383.html

Igor

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