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

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Message-ID: <CALCETrUh24L34ey3waq-QdJcy9OGAqdxcJXzvaN7FAoi+m4Dww@mail.gmail.com>
Date:	Tue, 27 Oct 2015 22:20:58 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	kvm list <kvm@...r.kernel.org>,
	Andy Lutomirski <luto@...nel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Rik van Riel <riel@...hat.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 Tue, Oct 27, 2015 at 6:39 PM, Paolo Bonzini <pbonzini@...hat.com> 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%.

Looks generally sensible.  I'm not familiar enough with the code to
call it reviewed-by while sitting on the airport shuttle.

--Andy
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