linux-kernel - Re: [PATCH] context_tracking: avoid extra checks on guest_enter and guest

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Date:	Wed, 29 Apr 2015 08:02:21 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org
CC:	fweisbec@...il.com, paulmck@...ux.vnet.ibm.com
Subject: Re: [PATCH] context_tracking: avoid extra checks on guest_enter and
 guest_exit

On 04/29/2015 05:21 AM, 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: 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>

... now time to figure out the same thing for user_enter
and/or user_exit, lets see which of those we can call
with irqs already disabled :)

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