From: Christian Borntraeger <borntraeger@de.ibm.com>
To: "Radim Krčmář" <rkrcmar@redhat.com>,
linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Cc: Christoffer Dall <cdall@linaro.org>,
Andrew Jones <drjones@redhat.com>,
Marc Zyngier <marc.zyngier@arm.com>,
Paolo Bonzini <pbonzini@redhat.com>,
Cornelia Huck <cornelia.huck@de.ibm.com>,
James Hogan <james.hogan@imgtec.com>,
Paul Mackerras <paulus@ozlabs.org>
Subject: Re: [PATCH 2/6] KVM: use kvm_{test,clear}_request instead of {test,clear}_bit
Date: Fri, 7 Apr 2017 12:55:15 +0200 [thread overview]
Message-ID: <e7609664-6d84-9602-1861-9d037e5953d2@de.ibm.com> (raw)
In-Reply-To: <20170406202056.18379-3-rkrcmar@redhat.com>
On 04/06/2017 10:20 PM, Radim Krčmář wrote:
> Users were expected to use kvm_check_request() for testing and clearing,
> but request have expanded their use since then and some users want to
> only test or do a faster clear.
>
> Make sure that requests are not directly accessed with bit operations, because
> we'll be clearing them later.
>
> Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
Patch itself looks sane
Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
one question:
> static inline bool kvm_check_request(int req, struct kvm_vcpu *vcpu)
> {
> - if (test_bit(req, &vcpu->requests)) {
> - clear_bit(req, &vcpu->requests);
> + if (kvm_test_request(req, vcpu)) {
> + kvm_clear_request(req, vcpu);
This looks fine. I am just asking myself why we do not use
test_and_clear_bit? Do we expect gcc to merge all test bits as
a fast path? This does not seem to work as far as I can tell and
almost everybody does a fast path like in
arch/s390/kvm/kvm-s390.c:
if (!vcpu->requests)
return 0;
arch/x86/kvm/x86.c:
if (vcpu->requests) {
>
> /*
> * Ensure the rest of the request is visible to kvm_check_request's
>
next prev parent reply other threads:[~2017-04-07 10:55 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-06 20:20 [PATCH 0/6] KVM: towards maintainable kvm_make_all_cpus_request() Radim Krčmář
2017-04-06 20:20 ` [PATCH RFC 1/6] KVM: fix guest_mode optimization in kvm_make_all_cpus_request() Radim Krčmář
2017-04-06 21:02 ` James Hogan
2017-04-10 15:59 ` Andrew Jones
2017-04-11 10:43 ` James Hogan
2017-04-11 5:25 ` Paolo Bonzini
2017-04-11 9:37 ` James Hogan
2017-04-11 19:31 ` Radim Krčmář
2017-04-11 19:45 ` Paolo Bonzini
2017-04-11 20:45 ` Radim Krčmář
2017-04-12 0:15 ` Paolo Bonzini
2017-04-07 10:47 ` Christian Borntraeger
2017-04-06 20:20 ` [PATCH 2/6] KVM: use kvm_{test,clear}_request instead of {test,clear}_bit Radim Krčmář
2017-04-07 10:55 ` Christian Borntraeger [this message]
2017-04-07 12:24 ` Radim Krčmář
2017-04-07 14:05 ` Radim Krčmář
2017-04-06 20:20 ` [PATCH 3/6] KVM: x86: use kvm_make_request instead of set_bit Radim Krčmář
2017-04-07 8:18 ` David Hildenbrand
2017-04-06 20:20 ` [PATCH 4/6] KVM: remove #ifndef CONFIG_S390 around kvm_vcpu_wake_up Radim Krčmář
2017-04-07 11:01 ` Christian Borntraeger
2017-04-06 20:20 ` [PATCH RFC 5/6] KVM: mark requests that do not need a wakeup Radim Krčmář
2017-04-07 8:27 ` Marc Zyngier
2017-04-07 12:29 ` Radim Krčmář
2017-04-06 20:20 ` [PATCH 6/6] KVM: perform a wake_up in kvm_make_all_cpus_request Radim Krčmář
2017-04-10 11:14 ` Andrew Jones
2017-04-11 5:34 ` Paolo Bonzini
2017-04-11 12:04 ` Andrew Jones
2017-04-11 5:37 ` Paolo Bonzini
2017-04-11 8:55 ` Paolo Bonzini
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