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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 18.10.12 at 10:22, Keir Fraser <keir@xxxxxxx> wrote:
> 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__

That wouldn't be correct: The function _is_ unused (and there's
no issue if it was used afaik), and the __used__ attribute ought
to tell the compiler to keep the function around despite not
having (visible to it) callers.

Jan

>> 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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>> Xen-devel@xxxxxxxxxxxxx 
>> http://lists.xen.org/xen-devel 




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