Message-ID: <e0a8ff65-b0f9-1f63-a3a0-2986eb79846f@amd.com>
Date:   Fri, 10 Feb 2023 09:58:55 +0530
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Subject: Re: [RFC PATCH 0/5] Memory access profiler(IBS) driven NUMA balancing
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To:     Dave Hansen <dave.hansen@intel.com>,
        Peter Zijlstra <peterz@infradead.org>
Cc:     linux-kernel@vger.kernel.org, linux-mm@kvack.org, mgorman@suse.de,
        mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com,
        x86@kernel.org, akpm@linux-foundation.org, luto@kernel.org,
        tglx@linutronix.de, yue.li@memverge.com,
        Ravikumar.Bangoria@amd.com, ying.huang@intel.com
References: <20230208073533.715-1-bharata@amd.com>
 <Y+Pj+9bbBbHpf6xM@hirez.programming.kicks-ass.net>
 <4808d3fa-bb68-d4c8-681f-0b2770d78041@intel.com>
 <369bef08-92cc-9b55-823f-1fe780532967@amd.com>
 <9848226e-2574-b8e0-4fb4-316957f57fb5@intel.com>
From:   Bharata B Rao <bharata@amd.com>
In-Reply-To: <9848226e-2574-b8e0-4fb4-316957f57fb5@intel.com>
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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/#)

Regards,
Bharata.