Re: [Qemu-devel] [PATCH 8/9] spapr_iommu: Introduce page_shift in sPAPRTCETable

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 05/22/2014 08:45 PM, Alexander Graf wrote:
> 
> On 22.05.14 12:24, Alexey Kardashevskiy wrote:
>> On 05/22/2014 08:09 PM, Alexander Graf wrote:
>>> On 22.05.14 01:45, Alexey Kardashevskiy wrote:
>>>> On 05/22/2014 08:11 AM, Alexander Graf wrote:
>>>>> On 21.05.14 16:21, Alexey Kardashevskiy wrote:
>>>>>> At the moment only 4K pages are supported by sPAPRTCETable. Since sPAPR
>>>>>> spec allows other page sizes and we are going to implement them, we need
>>>>>> page size to be configrable.
>>>>>>
>>>>>> This adds @page_shift into sPAPRTCETable and replaces
>>>>>> SPAPR_TCE_PAGE_SHIFT
>>>>>> with it whereever it is possible.
>>>>>>
>>>>>> This removes SPAPR_TCE_PAGE_MASK as it is no longer used.
>>>>>>
>>>>>> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> 
> [...]
> 
>>>>>> diff --git a/hw/ppc/spapr_pci.c b/hw/ppc/spapr_pci.c
>>>>>> index fdd4c07..c9850d4 100644
>>>>>> --- a/hw/ppc/spapr_pci.c
>>>>>> +++ b/hw/ppc/spapr_pci.c
>>>>>> @@ -656,6 +656,7 @@ static void spapr_phb_finish_realize(sPAPRPHBState
>>>>>> *sphb, Error **errp)
>>>>>>         sPAPRTCETable *tcet;
>>>>>>           tcet = spapr_tce_new_table(DEVICE(sphb), sphb->dma_liobn,
>>>>>> +                               SPAPR_TCE_PAGE_SHIFT,
>>>>>>                                    0x40000000 >> SPAPR_TCE_PAGE_SHIFT);
>>>>>>         if (!tcet) {
>>>>>>             error_setg(errp, "Unable to create TCE table for %s",
>>>>>> diff --git a/hw/ppc/spapr_vio.c b/hw/ppc/spapr_vio.c
>>>>>> index b84e481..d7e9e6a 100644
>>>>>> --- a/hw/ppc/spapr_vio.c
>>>>>> +++ b/hw/ppc/spapr_vio.c
>>>>>> @@ -457,6 +457,7 @@ static int spapr_vio_busdev_init(DeviceState *qdev)
>>>>>>         if (pc->rtce_window_size) {
>>>>>>             uint32_t liobn = SPAPR_VIO_BASE_LIOBN | dev->reg;
>>>>>>             dev->tcet = spapr_tce_new_table(qdev, liobn,
>>>>>> +                                        SPAPR_TCE_PAGE_SHIFT,
>>>>> I don't quite understand who defines what the TCE page size is for a
>>>>> given
>>>>> device. Can you try to explain this to me?
>>>> If it is default window (for PCI) or window for VIO - it is 4K. If it is a
>>>> dynamic DMA window - page size is a parameter of RTAS call which creates
>>>> the window.
>>> Could we change that default size for non-dynamic windows somehow? 4k is
>>> really fine grained.
>> No, this is hardcoded in a million places and old distros. Normally it is
>> maximum 1GB or 2MB table, not too bad. And with DDW support, we can make
>> the default one really small (64MB?) and lose even less.
>>
>> SPAPR:
>> R1–7.3.31–4. For the Dynamic DMA Windows (DDW) option: The platform must
>> provide a default DMA window
>> for each PE, and all of the following must be true:
>> a. The window is defined by the “ibm,dma-window” property in the OF device
>> tree.
>> b. The window is defined with 4 KB I/O pages.
>> c. The window is located entirely below 4 GB.
> 
> Cool, would be interesting to see how that affects performance. I like most
> of this patch set btw, I think it should be good to go in in the next round.


10Gbit ethernet is ok but 40Gbit seems to suffer from this limitation.



-- 
Alexey