linux-kernel - Re: [PATCH RFC 5/6] KVM: mark requests that do not need a wakeup

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Message-ID: <eab3a2dd-3ade-57f2-ec2b-1ebd744df0fa@arm.com>
Date:   Fri, 7 Apr 2017 09:27:00 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     Radim Krčmář <rkrcmar@...hat.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Christoffer Dall <cdall@...aro.org>,
        Andrew Jones <drjones@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Cornelia Huck <cornelia.huck@...ibm.com>,
        James Hogan <james.hogan@...tec.com>,
        Paul Mackerras <paulus@...abs.org>
Subject: Re: [PATCH RFC 5/6] KVM: mark requests that do not need a wakeup

On 06/04/17 21:20, Radim Krčmář wrote:
> Some operations must ensure that the guest is not running with stale
> data, but if the guest is halted, then the update can wait until another
> event happens.  kvm_make_all_requests() currently doesn't wake up, so we
> can mark all requests used with it.
> 
> First 8 bits were arbitrarily reserved for request numbers.
> 
> Most uses of requests have the request type as a constant, so a compiler
> will optimize the '&'.
> 
> An alternative would be to have an inline function that would return
> whether the request needs a wake-up or not, but I like this one better
> even though it might produce worse assembly.
> 
> Suggested-by: Christoffer Dall <cdall@...aro.org>
> Signed-off-by: Radim Krčmář <rkrcmar@...hat.com>
> ---
>   Btw. do you recall which macro allowed to define bitmasks?  (It has
>   two arguments, FROM and TO.)

GENMASK (and its _ULL variant), defined in include/linux/bitops.h.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...