linux-kernel - Re: [RFC PATCH v4 00/19] Core scheduling v4

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Date:   Wed, 5 Feb 2020 16:28:18 -0800
From:   Tim Chen <tim.c.chen@...ux.intel.com>
To:     Vineeth Remanan Pillai <vpillai@...italocean.com>
Cc:     Nishanth Aravamudan <naravamudan@...italocean.com>,
        Julien Desfossez <jdesfossez@...italocean.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Paul Turner <pjt@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Dario Faggioli <dfaggioli@...e.com>,
        Frédéric Weisbecker <fweisbec@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Greg Kerr <kerrnel@...gle.com>, Phil Auld <pauld@...hat.com>,
        Aaron Lu <aaron.lwe@...il.com>,
        Aubrey Li <aubrey.intel@...il.com>,
        Valentin Schneider <valentin.schneider@....com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [RFC PATCH v4 00/19] Core scheduling v4

On 1/14/20 7:40 AM, Vineeth Remanan Pillai wrote:
> On Mon, Jan 13, 2020 at 8:12 PM Tim Chen <tim.c.chen@...ux.intel.com> wrote:
> 
>> I also encountered kernel panic with the v4 code when taking cpu offline or online
>> when core scheduler is running.  I've refreshed the previous patch, along
>> with 3 other patches to fix problems related to CPU online/offline.
>>
>> As a side effect of the fix, each core can now operate in core-scheduling
>> mode or non core-scheduling mode, depending on how many online SMT threads it has.
>>
>> Vineet, are you guys planning to refresh v4 and update it to v5?  Aubrey posted
>> a port to the latest kernel earlier.
>>
> Thanks for the updated patch Tim.
> 
> We have been testing with v4 rebased on 5.4.8 as RC kernels had given us
> trouble in the past. v5 is due soon and we are planning to release v5 when
> 5.5 comes out. As of now, v5 has your crash fixes and Aubrey's changes
> related to load balancing. We are investigating a performance issue with
> high overcommit io intensive workload and also we are trying to see if
> we can add synchronization during VMEXITs so that a guest vm cannot run
> run alongside with host kernel. We also need to think about the userland
> interface for corescheduling in preparation for upstreaming work.
> 

Vineet,

Have you guys been able to make progress on the issues with I/O intensive workload?

Can you explain a bit further what the problem is?  
Is the VM doing lots of I/O, causing frequent VMEXITs?
And the the host thread doing the I/O cannot run along side with vcpu
thread, resulting in extra forced idle?  So you are trying not to put vcpu
on the same core with such host thread?

Tim