Re: [Qemu-devel] [PATCH V4 4/4] target-i386: add i440fx 0xcf8 portascoalesced_pio

[peng.hao2]

>On Mon, Aug 27, 2018 at 04:25:00PM +0800, address@hidden wrote:
>> >> On 25 Aug 2018, at 15:19, Peng Hao <address@hidden> wrote:
>> >> 
>> >> diff --git a/hw/pci-host/piix.c b/hw/pci-host/piix.c
>> >> index 0e60834..da73743 100644
>> >> --- a/hw/pci-host/piix.c
>> >> +++ b/hw/pci-host/piix.c
>> >> @@ -327,6 +327,10 @@ static void i440fx_pcihost_realize(DeviceState *dev, 
>> >> Error **errp)
>> >> 
>> >>     sysbus_add_io(sbd, 0xcfc, &s->data_mem);
>> >>     sysbus_init_ioports(sbd, 0xcfc, 4);
>> >> +
>> >> +    /* register i440fx 0xcf8 port as coalesced pio */
>> >> +    memory_region_set_flush_coalesced(&s->data_mem);
>> >> +    memory_region_add_coalescing(&s->conf_mem, 0, 4);
>> >> }
>> >> 
>> >Is there a reason to not register this port as coalesced PIO also for Q35?
>> >In q35_host_realize()?
>> >If not, I would do that as an extra patch as part of this series.
>> Just as I mentioned in patch [0/4] , you can add pci->>host config port as 
>> coalesecd pio. I think  it works for q35 port 0xcf8.
>> >-Liran
>
>What's the performance improvement for q35?
q35 also has  the same pci-host config port 0xcf8  as  piix. I test the 
coalesced pio for 
q35 pci-host config port 0xcf8. It spent less VM-exit avg time from 3us to 
0.6us.

>-- 
>MST