linux-kernel - Re: [RFC PATCH 0/7] Add support for monitoring guest TLB operations

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Message-ID: <a553745d-a527-b2ba-7cfa-f688786d5dc3@redhat.com>
Date:	Wed, 17 Aug 2016 19:02:32 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Punit Agrawal <punit.agrawal@....com>
Cc:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	kvmarm@...ts.cs.columbia.edu, linux-arm-kernel@...ts.infradead.org,
	Marc Zyngier <marc.zyngier@....com>,
	Ingo Molnar <mingo@...hat.com>,
	Will Deacon <will.deacon@....com>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [RFC PATCH 0/7] Add support for monitoring guest TLB operations



On 17/08/2016 19:01, Punit Agrawal wrote:
>> Can you explain what this is used for?  In other words, why would this
>> be used instead of just running perf in the guest?
> 
> As TLB maintenance operations are synchronised in hardware, they can
> impact performance beyond the guest. The operations generate traffic on
> the interconnect and depending on the implementation, they can also
> affect the remote TLB's translation bandwidth.
> 
> These patches are useful on systems where the host and guest are
> controlled by different users - the guest could be running arbitrary
> software. 
> 
> Having the ability to monitor the usage of guest TLB invalidations in
> the host can be useful to diagnose performance issues on such systems.

Are there hardware performance counters for these operations?

Paolo