Re: [Qemu-devel] [PULL 7/9] KVM: Retry KVM_CREATE_VM on EINTR

[Alexander Graf]

On 20.01.2014, at 15:44, Paolo Bonzini <address@hidden> wrote:

> From: thomas knych <address@hidden>
> 
> Upstreaming this change from Android 
> (https://android-review.googlesource.com/54211).
> 
> On heavily loaded machines with many VM instances we see KVM_CREATE_VM
> failing with EINTR on this path:
> 
> kvm_dev_ioctl_create_vm -> kvm_create_vm -> kvm_init_mmu_notifier -> 
> mmu_notifier_register ->  do_mmu_notifier_register -> mm_take_all_locks
> 
> which checks if any signals have been raised while it was attaining locks
> and returns EINTR.  Retrying the system call greatly improves reliability.
> 
> Cc: address@hidden
> Signed-off-by: thomas knych <address@hidden>
> Signed-off-by: Paolo Bonzini <address@hidden>
> ---
> kvm-all.c | 12 +++++++++---
> 1 file changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/kvm-all.c b/kvm-all.c
> index 3937754..6df2ee1 100644
> --- a/kvm-all.c
> +++ b/kvm-all.c
> @@ -1442,16 +1442,22 @@ int kvm_init(void)
>         nc++;
>     }
> 
> -    s->vmfd = kvm_ioctl(s, KVM_CREATE_VM, 0);
> -    if (s->vmfd < 0) {
> +    do {
> +        ret = kvm_ioctl(s, KVM_CREATE_VM, 0);
> +    } while (ret == -EINTR);
> +
> +    if (ret < 0) {
> +        fprintf(stderr, "ioctl(KVM_CREATE_VM) failed: %d %s\n", -s->vmfd,

Shouldn't this be -ret?


Alex

> +                strerror(-ret));
> +
> #ifdef TARGET_S390X
>         fprintf(stderr, "Please add the 'switch_amode' kernel parameter to "
>                         "your host kernel command line\n");
> #endif
> -        ret = s->vmfd;
>         goto err;
>     }
> 
> +    s->vmfd = ret;
>     missing_cap = kvm_check_extension_list(s, kvm_required_capabilites);
>     if (!missing_cap) {
>         missing_cap =
> -- 
> 1.8.3.1
> 
> 
>