linux-kernel - Re: [PATCH 2/3] context_tracking: avoid irq_save/irq

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Date:	Mon, 09 Nov 2015 08:58:22 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org
CC:	Andy Lutomirski <luto@...nel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH 2/3] context_tracking: avoid irq_save/irq_restore on guest
 entry and exit

On 10/27/2015 09:39 PM, Paolo Bonzini wrote:
> guest_enter and guest_exit must be called with interrupts disabled,
> since they take the vtime_seqlock with write_seq{lock,unlock}.
> Therefore, it is not necessary to check for exceptions, nor to
> save/restore the IRQ state, when context tracking functions are
> called by guest_enter and guest_exit.
> 
> Split the body of context_tracking_entry and context_tracking_exit
> out to __-prefixed functions, and use them from KVM.
> 
> Rik van Riel has measured this to speed up a tight vmentry/vmexit
> loop by about 2%.
> 
> Cc: Andy Lutomirski <luto@...nel.org>
> Cc: Frederic Weisbecker <fweisbec@...il.com>
> Cc: Rik van Riel <riel@...hat.com>
> Cc: Paul McKenney <paulmck@...ux.vnet.ibm.com>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>

Reviewed-by: Rik van Riel <riel@...hat.com>
Tested-by: Rik van Riel <riel@...hat.com>

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