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Subject: Re: Gang scheduling
To:     Subhra Mazumdar <subhra.mazumdar@oracle.com>,
        linux-kernel@vger.kernel.org
Cc:     Peter Zijlstra <peterz@infradead.org>
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From:   Tim Chen <tim.c.chen@linux.intel.com>
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Message-ID: <70d78b14-53a6-4523-856b-e67139a55a58@linux.intel.com>
Date:   Wed, 13 Feb 2019 10:25:09 -0800
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On 2/12/19 6:57 PM, Subhra Mazumdar wrote:
> Hi Tim,
> 
> On 10/12/18 11:01 AM, Tim Chen wrote:
>> On 10/10/2018 05:09 PM, Subhra Mazumdar wrote:
>>> Hi,
>>>
>>> I was following the Coscheduling patch discussion on lkml and Peter mentioned he had a patch series. I found the following on github.
>>>
>>> https://github.com/pdxChen/gang/commits/sched_1.23-loadbal
>>>
>>> I would like to test this with KVMs. Are the commits from 38d5acb to f019876 sufficient? Also is there any documentaion on how to use it (any knobs I need to turn on for gang scheduling to happen?) or is it enabled by default for KVMs?
>>>
>>> Thanks,
>>> Subhra
>>>
>> I would suggest you try
>> https://github.com/pdxChen/gang/tree/sched_1.23-base
>> without the load balancing part of gang scheduling.
>> It is enabled by default for KVMs.
> I applied the following 3 patches on 4.19 and tried to install a KVM (with
> virt-install). But the kernel hangs with following error:
> 
> kernel:watchdog: BUG: soft lockup - CPU#21 stuck for 23s! [kworker/21:1:573]
> 
> kvm,sched: Track VCPU threads
> x86/kvm,sched: Add fast path for reschedule interrupt
> sched: Optimize scheduler_ipi()
> 
> The track VCPU patch seems to be the culprit.
> 
> Thanks,
> Subhra

Thanks for giving it a try.  Peter is working on a new version.  So I'll not try
to debug this patchset for now.

Tim