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Re: [Xen-devel] [PATCH 4/5] xen: use masking operation instead of test_bit for VPF bits



On 02/10/15 05:40, Juergen Gross wrote:
> Use a bit mask for testing of a set bit instead of test_bit in case no
> atomic operation is needed, as this will lead to smaller and more
> effective code.
> 
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>

On a side note, a handful of functions seem to access the vcpu structure
with the *domain* lock held, rather than the *scheduler* lock; for example:

xen/arch/x86/hvm/vlapic.c:vlapic_accept_irq()
xen/common/domain.c:vcpu_reset()

Is this a bug (perhaps left over from when we used the domain lock for
vcpus rather than the scheduler lock)?

 -George

> ---
>  xen/arch/x86/domctl.c  |  2 +-
>  xen/arch/x86/hvm/hvm.c |  4 ++--
>  xen/arch/x86/hvm/vpt.c |  2 +-
>  xen/common/domain.c    |  4 ++--
>  xen/common/domctl.c    |  8 ++++----
>  xen/common/schedule.c  | 16 ++++++++--------
>  6 files changed, 18 insertions(+), 18 deletions(-)
> 
> diff --git a/xen/arch/x86/domctl.c b/xen/arch/x86/domctl.c
> index 6172c0d..f8a559c 100644
> --- a/xen/arch/x86/domctl.c
> +++ b/xen/arch/x86/domctl.c
> @@ -1213,7 +1213,7 @@ void arch_get_info_guest(struct vcpu *v, 
> vcpu_guest_context_u c)
>      c(flags = v->arch.vgc_flags & ~(VGCF_i387_valid|VGCF_in_kernel));
>      if ( v->fpu_initialised )
>          c(flags |= VGCF_i387_valid);
> -    if ( !test_bit(_VPF_down, &v->pause_flags) )
> +    if ( !(v->pause_flags & VPF_down) )
>          c(flags |= VGCF_online);
>      if ( !compat )
>      {
> diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
> index 6afc344..3fa2280 100644
> --- a/xen/arch/x86/hvm/hvm.c
> +++ b/xen/arch/x86/hvm/hvm.c
> @@ -1728,7 +1728,7 @@ static int hvm_save_cpu_ctxt(struct domain *d, 
> hvm_domain_context_t *h)
>      {
>          /* We don't need to save state for a vcpu that is down; the restore 
>           * code will leave it down if there is nothing saved. */
> -        if ( test_bit(_VPF_down, &v->pause_flags) ) 
> +        if ( v->pause_flags & VPF_down )
>              continue;
>  
>          /* Architecture-specific vmcs/vmcb bits */
> @@ -2512,7 +2512,7 @@ void hvm_vcpu_down(struct vcpu *v)
>      /* Any other VCPUs online? ... */
>      domain_lock(d);
>      for_each_vcpu ( d, v )
> -        if ( !test_bit(_VPF_down, &v->pause_flags) )
> +        if ( !(v->pause_flags & VPF_down) )
>              online_count++;
>      domain_unlock(d);
>  
> diff --git a/xen/arch/x86/hvm/vpt.c b/xen/arch/x86/hvm/vpt.c
> index 0c8b22e..4fa6566 100644
> --- a/xen/arch/x86/hvm/vpt.c
> +++ b/xen/arch/x86/hvm/vpt.c
> @@ -178,7 +178,7 @@ void pt_save_timer(struct vcpu *v)
>      struct list_head *head = &v->arch.hvm_vcpu.tm_list;
>      struct periodic_time *pt;
>  
> -    if ( test_bit(_VPF_blocked, &v->pause_flags) )
> +    if ( v->pause_flags & VPF_blocked )
>          return;
>  
>      spin_lock(&v->arch.hvm_vcpu.tm_lock);
> diff --git a/xen/common/domain.c b/xen/common/domain.c
> index cda60a9..7c362eb 100644
> --- a/xen/common/domain.c
> +++ b/xen/common/domain.c
> @@ -1135,7 +1135,7 @@ int map_vcpu_info(struct vcpu *v, unsigned long gfn, 
> unsigned offset)
>          return -EINVAL;
>  
>      /* Run this command on yourself or on other offline VCPUS. */
> -    if ( (v != current) && !test_bit(_VPF_down, &v->pause_flags) )
> +    if ( (v != current) && !(v->pause_flags & VPF_down) )
>          return -EINVAL;
>  
>      page = get_page_from_gfn(d, gfn, NULL, P2M_ALLOC);
> @@ -1263,7 +1263,7 @@ long do_vcpu_op(int cmd, unsigned int vcpuid, 
> XEN_GUEST_HANDLE_PARAM(void) arg)
>          break;
>  
>      case VCPUOP_is_up:
> -        rc = !test_bit(_VPF_down, &v->pause_flags);
> +        rc = !(v->pause_flags & VPF_down);
>          break;
>  
>      case VCPUOP_get_runstate_info:
> diff --git a/xen/common/domctl.c b/xen/common/domctl.c
> index 08de32d..46b967e 100644
> --- a/xen/common/domctl.c
> +++ b/xen/common/domctl.c
> @@ -170,7 +170,7 @@ void getdomaininfo(struct domain *d, struct 
> xen_domctl_getdomaininfo *info)
>          vcpu_runstate_get(v, &runstate);
>          cpu_time += runstate.time[RUNSTATE_running];
>          info->max_vcpu_id = v->vcpu_id;
> -        if ( !test_bit(_VPF_down, &v->pause_flags) )
> +        if ( !(v->pause_flags & VPF_down) )
>          {
>              if ( !(v->pause_flags & VPF_blocked) )
>                  flags &= ~XEN_DOMINF_blocked;
> @@ -231,7 +231,7 @@ static unsigned int default_vcpu0_location(cpumask_t 
> *online)
>          rcu_read_lock(&domlist_read_lock);
>          for_each_domain ( d )
>              for_each_vcpu ( d, v )
> -                if ( !test_bit(_VPF_down, &v->pause_flags)
> +                if ( !(v->pause_flags & VPF_down)
>                       && ((cpu = v->processor) < nr_cpus) )
>                      cnt[cpu]++;
>          rcu_read_unlock(&domlist_read_lock);
> @@ -944,8 +944,8 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xen_domctl_t) 
> u_domctl)
>  
>          vcpu_runstate_get(v, &runstate);
>  
> -        op->u.getvcpuinfo.online   = !test_bit(_VPF_down, &v->pause_flags);
> -        op->u.getvcpuinfo.blocked  = test_bit(_VPF_blocked, &v->pause_flags);
> +        op->u.getvcpuinfo.online   = !(v->pause_flags & VPF_down);
> +        op->u.getvcpuinfo.blocked  = !!(v->pause_flags & VPF_blocked);
>          op->u.getvcpuinfo.running  = v->is_running;
>          op->u.getvcpuinfo.cpu_time = runstate.time[RUNSTATE_running];
>          op->u.getvcpuinfo.cpu      = v->processor;
> diff --git a/xen/common/schedule.c b/xen/common/schedule.c
> index 5ffa1a1..c5f640f 100644
> --- a/xen/common/schedule.c
> +++ b/xen/common/schedule.c
> @@ -119,7 +119,7 @@ static inline void vcpu_urgent_count_update(struct vcpu 
> *v)
>  
>      if ( unlikely(v->is_urgent) )
>      {
> -        if ( !test_bit(_VPF_blocked, &v->pause_flags) ||
> +        if ( !(v->pause_flags & VPF_blocked) ||
>               !test_bit(v->vcpu_id, v->domain->poll_mask) )
>          {
>              v->is_urgent = 0;
> @@ -128,8 +128,8 @@ static inline void vcpu_urgent_count_update(struct vcpu 
> *v)
>      }
>      else
>      {
> -        if ( unlikely(test_bit(_VPF_blocked, &v->pause_flags) &&
> -                      test_bit(v->vcpu_id, v->domain->poll_mask)) )
> +        if ( unlikely(v->pause_flags & VPF_blocked) &&
> +             unlikely(test_bit(v->vcpu_id, v->domain->poll_mask)) )
>          {
>              v->is_urgent = 1;
>              atomic_inc(&per_cpu(schedule_data,v->processor).urgent_count);
> @@ -418,7 +418,7 @@ void vcpu_wake(struct vcpu *v)
>              vcpu_runstate_change(v, RUNSTATE_runnable, NOW());
>          SCHED_OP(VCPU2OP(v), wake, v);
>      }
> -    else if ( !test_bit(_VPF_blocked, &v->pause_flags) )
> +    else if ( !(v->pause_flags & VPF_blocked) )
>      {
>          if ( v->runstate.state == RUNSTATE_blocked )
>              vcpu_runstate_change(v, RUNSTATE_offline, NOW());
> @@ -595,7 +595,7 @@ void vcpu_force_reschedule(struct vcpu *v)
>          set_bit(_VPF_migrating, &v->pause_flags);
>      vcpu_schedule_unlock_irq(lock, v);
>  
> -    if ( test_bit(_VPF_migrating, &v->pause_flags) )
> +    if ( v->pause_flags & VPF_migrating )
>      {
>          vcpu_sleep_nosync(v);
>          vcpu_migrate(v);
> @@ -763,7 +763,7 @@ static int vcpu_set_affinity(
>  
>      domain_update_node_affinity(v->domain);
>  
> -    if ( test_bit(_VPF_migrating, &v->pause_flags) )
> +    if ( v->pause_flags & VPF_migrating )
>      {
>          vcpu_sleep_nosync(v);
>          vcpu_migrate(v);
> @@ -1285,7 +1285,7 @@ static void schedule(void)
>  
>      vcpu_runstate_change(
>          prev,
> -        (test_bit(_VPF_blocked, &prev->pause_flags) ? RUNSTATE_blocked :
> +        ((prev->pause_flags & VPF_blocked) ? RUNSTATE_blocked :
>           (vcpu_runnable(prev) ? RUNSTATE_runnable : RUNSTATE_offline)),
>          now);
>      prev->last_run_time = now;
> @@ -1327,7 +1327,7 @@ void context_saved(struct vcpu *prev)
>  
>      SCHED_OP(VCPU2OP(prev), context_saved, prev);
>  
> -    if ( unlikely(test_bit(_VPF_migrating, &prev->pause_flags)) )
> +    if ( unlikely(prev->pause_flags & VPF_migrating) )
>          vcpu_migrate(prev);
>  }
>  
> 


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