linux-kernel - Re: [RFC PATCH 0/5] Memory access profiler(IBS) driven NUMA balancing

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Date:   Thu, 9 Feb 2023 20:40:09 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Bharata B Rao <bharata@....com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org, mgorman@...e.de,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        x86@...nel.org, akpm@...ux-foundation.org, luto@...nel.org,
        tglx@...utronix.de, yue.li@...verge.com,
        Ravikumar.Bangoria@....com, ying.huang@...el.com
Subject: Re: [RFC PATCH 0/5] Memory access profiler(IBS) driven NUMA balancing

On 2/9/23 20:28, Bharata B Rao wrote:
> On 2/9/2023 7:58 PM, Dave Hansen wrote:
>> On 2/8/23 22:04, Bharata B Rao wrote:
>>>> First, IIRC, Intel PEBS at the time only gave guest virtual addresses in
>>>> the PEBS records.  They had to be translated back to host addresses to
>>>> be usable.  That was extra expensive.
>>> Just to be clear, I am using IBS in host only and it can give both virtual
>>> and physical address.
>> Could you talk a little bit about how IBS might get used for NUMA
>> balancing guest memory?
> IBS can work for guest, but will not provide physical address. Also
> the support for virtualized IBS isn't upstream yet.
> 
> However I am not sure how effective or useful NUMA balancing within a guest
> is, as the actual physical addresses are transparent to the guest.
> 
> Additionally when using IBS in host, it is possible to prevent collection
> of samples from secure guests by using the PreventHostIBS feature.
> (https://lore.kernel.org/linux-perf-users/20230206060545.628502-1-manali.shukla@amd.com/T/#)
I was wondering specifically about how a host might use IBS to balance
guest memory transparently to the guest.  Now how a guest might use IBS
to balance its own memory.