Re: [RFC PATCH kernel] Revert "net/mlx4_core: Set UAR page size to 4KB regardless of system page size"

Alexey Kardashevskiy
2016-03-16T05:49:13Z

On 03/16/2016 04:10 PM, Eli Cohen wrote:
> On Wed, Mar 16, 2016 at 01:07:58PM +1100, Alexey Kardashevskiy wrote:
>>
>> So with v4.5 as a host, there is no actual distro available today to
>> use as a guest in the next 6 months (or whatever it takes to
>> backport this partucular patch back there).
>>
>> You could have added a module parameter to enforce the old behavoir,
>> at least...
>>
>> And sorry but from the original commit log I could not understand
>> why exactly all existing guests need to be broken. Could you please
>> point me to a piece of documentation describing all this UAR
>> bisuness (what is UAR, why 128 UARs are required and for what, etc).
>> Thanks.
>>
>
> We are going to send a patch that fixes this using a module parameter.
> The patch will be on top of Huy's patch.
>
> Some background to the problem: mlx4 supported devices require 128 UAR

What does UAR stand for?

> pages from PCI memory space defined by BAR2-3. Each UAR page can be
> any power of 2 value from 4K up to 64K. Before Huy's patch the driver
> chose UAR page size to be equal to system page size. Since PowerPC's
> page size is 64K this means minimum requirement of UAR pages is not
> met (default UAR BAR is 8MB and only half of it is really reserved for
> UARs).

And what was the downside? afaict the performance was good...

> More details can be found in the programmer's manual.

Can you please point me to this manual on the website? I tried, honestly,
could not find it. Thanks.

--
Alexey