lkml.org 
[lkml]   [2012]   [Jun]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCHv7 3/8] kvm_para: guest side for eoi avoidance
    On Mon, Jun 18, 2012 at 05:17:24PM +0300, Avi Kivity wrote:
    > On 06/14/2012 04:53 PM, Michael S. Tsirkin wrote:
    > > The idea is simple: there's a bit, per APIC, in guest memory,
    > > that tells the guest that it does not need EOI.
    > > Guest tests it using a single est and clear operation - this is
    > > necessary so that host can detect interrupt nesting - and if set, it can
    > > skip the EOI MSR.
    > >
    > > I run a simple microbenchmark to show exit reduction
    > > (note: for testing, need to apply follow-up patch
    > > 'kvm: host side for eoi optimization' + a qemu patch
    > > I posted separately, on host):
    > >
    > >
    > > diff --git a/arch/x86/include/asm/bitops.h b/arch/x86/include/asm/bitops.h
    > > index a6983b2..47f9eff 100644
    > > --- a/arch/x86/include/asm/bitops.h
    > > +++ b/arch/x86/include/asm/bitops.h
    > > @@ -28,11 +28,13 @@
    > > #if __GNUC__ < 4 || (__GNUC__ == 4 && __GNUC_MINOR__ < 1)
    > > /* Technically wrong, but this avoids compilation errors on some gcc
    > > versions. */
    > > -#define BITOP_ADDR(x) "=m" (*(volatile long *) (x))
    > > +#define BITOP_ADDR_CONSTRAINT "=m"
    > > #else
    > > -#define BITOP_ADDR(x) "+m" (*(volatile long *) (x))
    > > +#define BITOP_ADDR_CONSTRAINT "+m"
    > > #endif
    > >
    > > +#define BITOP_ADDR(x) BITOP_ADDR_CONSTRAINT (*(volatile long *) (x))
    > > +
    > > #define ADDR BITOP_ADDR(addr)
    >
    > What's this doing here?

    Ugh. More leftovers from when I had inline asm here.
    Will remove.

    > >
    > > +/* size alignment is implied but just to make it explicit. */
    > > +static DEFINE_PER_CPU(unsigned long, kvm_apic_eoi) __aligned(2) =
    > > + KVM_PV_EOI_DISABLED;
    >
    > You're actually breaking the alignment. ulong has 8 byte alignment
    > sometimes and you can make it cross cache boundary this way.

    No, if you look at the definition of __aligned
    you will see that it limits the alignment from below.
    Compiler still applies the natural size alignment.
    You are not the first to get confused. So I wonder: is it better
    to add a comment or simply remove __aligned here.

    > > +
    > > void __cpuinit kvm_guest_cpu_init(void)
    > > {
    > > if (!kvm_para_available())
    > > @@ -300,11 +320,17 @@ void __cpuinit kvm_guest_cpu_init(void)
    > > smp_processor_id());
    > > }
    > >
    > > + if (kvm_para_has_feature(KVM_FEATURE_PV_EOI)) {
    > > + __get_cpu_var(kvm_apic_eoi) = 0;
    > > + wrmsrl(MSR_KVM_PV_EOI_EN, __pa(&__get_cpu_var(kvm_apic_eoi)) |
    > > + KVM_MSR_ENABLED);
    >
    > Bad formatting.

    I guess temporary will make it prettier.
    unsigned long pa;
    __get_cpu_var(kvm_apic_eoi) = 0;
    pa = __pa(&__get_cpu_var(kvm_apic_eoi)) | KVM_MSR_ENABLED;
    wrmsrl(MSR_KVM_PV_EOI_EN, pa);

    or did I miss the point?

    > > + }
    > > +
    > > if (has_steal_clock)
    > > kvm_register_steal_time();
    > > }
    > >
    >
    >
    > Please check that the kexec path also disables pveoi.

    The chunk in kvm_pv_guest_cpu_reboot does this, doesn't it?

    > --
    > error compiling committee.c: too many arguments to function
    >


    \
     
     \ /
      Last update: 2012-06-18 17:21    [W:3.869 / U:0.428 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site