Re: [Xen-devel] [PATCH 3/3] x86/HPET: cache MSI message last written

[Keir Fraser <keir@xxxxxxx>]

On 16/10/2012 16:11, "Jan Beulich" <JBeulich@xxxxxxxx> wrote:

> Rather than spending measurable amounts of time reading back the most
> recently written message, cache it in space previously unused, and thus
> accelerate the CPU's entering of the intended C-state.
> 
> hpet_msi_read() ends up being unused after this change, but rather than
> removing the function, it's being marked "unused" in order - that way
> it can easily get used again should a new need for it arise.

Please use __attribute_used__

> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

Acked-by: Keir Fraser <keir@xxxxxxx>

> --- a/xen/arch/x86/hpet.c
> +++ b/xen/arch/x86/hpet.c
> @@ -253,17 +253,19 @@ static void hpet_msi_mask(struct irq_des
>  
>  static void hpet_msi_write(struct hpet_event_channel *ch, struct msi_msg
> *msg)
>  {
> +    ch->msi.msg = *msg;
>      if ( iommu_intremap )
>          iommu_update_ire_from_msi(&ch->msi, msg);
>      hpet_write32(msg->data, HPET_Tn_ROUTE(ch->idx));
>      hpet_write32(msg->address_lo, HPET_Tn_ROUTE(ch->idx) + 4);
>  }
>  
> -static void hpet_msi_read(struct hpet_event_channel *ch, struct msi_msg *msg)
> +static void __attribute__((__unused__))
> +hpet_msi_read(struct hpet_event_channel *ch, struct msi_msg *msg)
>  {
>      msg->data = hpet_read32(HPET_Tn_ROUTE(ch->idx));
>      msg->address_lo = hpet_read32(HPET_Tn_ROUTE(ch->idx) + 4);
> -    msg->address_hi = 0;
> +    msg->address_hi = MSI_ADDR_BASE_HI;
>      if ( iommu_intremap )
>          iommu_read_msi_from_ire(&ch->msi, msg);
>  }
> @@ -285,20 +287,19 @@ static void hpet_msi_ack(struct irq_desc
>  
>  static void hpet_msi_set_affinity(struct irq_desc *desc, const cpumask_t
> *mask)
>  {
> -    struct msi_msg msg;
> -    unsigned int dest;
> +    struct hpet_event_channel *ch = desc->action->dev_id;
> +    struct msi_msg msg = ch->msi.msg;
>  
> -    dest = set_desc_affinity(desc, mask);
> -    if (dest == BAD_APICID)
> +    msg.dest32 = set_desc_affinity(desc, mask);
> +    if ( msg.dest32 == BAD_APICID )
>          return;
>  
> -    hpet_msi_read(desc->action->dev_id, &msg);
>      msg.data &= ~MSI_DATA_VECTOR_MASK;
>      msg.data |= MSI_DATA_VECTOR(desc->arch.vector);
>      msg.address_lo &= ~MSI_ADDR_DEST_ID_MASK;
> -    msg.address_lo |= MSI_ADDR_DEST_ID(dest);
> -    msg.dest32 = dest;
> -    hpet_msi_write(desc->action->dev_id, &msg);
> +    msg.address_lo |= MSI_ADDR_DEST_ID(msg.dest32);
> +    if ( msg.data != ch->msi.msg.data || msg.dest32 != ch->msi.msg.dest32 )
> +        hpet_msi_write(ch, &msg);
>  }
>  
>  /*
> 
> 
> 
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