On Sun, May 20, 2012 at 04:49:27PM +0300, Avi Kivity wrote:
> Instead of using a atomic operation per active request, use just one
> to get all requests at once, then check them with local ops. This
> probably isn't any faster, since simultaneous requests are rare, but
> it does reduce code size.
>
> Signed-off-by: Avi Kivity <avi@xxxxxxxxxx>
> ---
> arch/x86/kvm/x86.c | 33 ++++++++++++++++++---------------
> 1 file changed, 18 insertions(+), 15 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 953e692..c0209eb 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -5232,55 +5232,58 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
> bool req_int_win = !irqchip_in_kernel(vcpu->kvm) &&
> vcpu->run->request_interrupt_window;
> bool req_immediate_exit = 0;
> + ulong reqs;
>
> if (unlikely(req_int_win))
> kvm_make_request(KVM_REQ_EVENT, vcpu);
>
> if (vcpu->requests) {
> - if (kvm_check_request(KVM_REQ_MMU_RELOAD, vcpu))
> + reqs = xchg(&vcpu->requests, 0UL);
> +
> + if (test_bit(KVM_REQ_MMU_RELOAD, &reqs))
> kvm_mmu_unload(vcpu);
> - if (kvm_check_request(KVM_REQ_MIGRATE_TIMER, vcpu))
> + if (test_bit(KVM_REQ_MIGRATE_TIMER, &reqs))
> __kvm_migrate_timers(vcpu);
> - if (kvm_check_request(KVM_REQ_CLOCK_UPDATE, vcpu)) {
> + if (test_bit(KVM_REQ_CLOCK_UPDATE, &reqs)) {
> r = kvm_guest_time_update(vcpu);
> if (unlikely(r))
> goto out;
> }
Bailing out loses requests in "reqs".
Caching the requests makes the following type of sequence behave strangely
req = xchg(&vcpu->requests);
if request is set
request handler
...
set REQ_EVENT
...
prepare for guest entry
vcpu->requests set
bail
The code is more straightforward as it is.
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