Re: [RFC] Start SMP subsystem earlier

On 6 January 2015 at 07:55, Ian Lepore <ian_at_freebsd.org> wrote:
> On Tue, 2015-01-06 at 09:37 -0500, John Baldwin wrote:
>> On 1/5/15 8:18 AM, Hans Petter Selasky wrote:
>> > Hi,
>> >
>> > There is a limitiation on the number of interrupt vectors available when
>> > only a single processor is running. To have more interrupts available we
>> > need to start SMP earlier when building a monotolith kernel and not
>> > loading drivers as modules. The driver in question is a network driver
>> > and because it cannot be started after SI_SUB_ROOT_CONF due to PXE
>> > support I see no other option than to move SI_SUB_SMP earlier.
>> >
>> > Suggested patch:
>> >
>> >>[...]
>> >
>> > This fixes a problem for Mellanox drivers in the OFED layer. Possibly we
>> > need to move the SMP even earlier to not miss the generic FreeBSD PCI
>> > device enumeration or maybe this is not possible. Does anyone know how
>> > early we can start SMP?
>>
>> We need a lot more work before this is ready.  This is one of the goals
>> of the multipass new-bus stuff.  In particular, we have to enumerate
>> enough devices to bring event timer hardware up so that timer interrupts
>> work so that tsleep() will actually sleep.  In addition, we also need
>> idle threads created and working before APs are started as otherwise
>> they will have no thread to run initially.  This is certainly a desired
>> feature, but it is not as simple as moving the sysinit up I'm afraid.
>>
>
> Just an FYI, the ARM world is now using the multipass newbus stuff.  It
> works well, with some quirks...
>
> The predefined pass names don't always makes sense for the arm world.
> There aren't enough predefined pass names and even though the number
> space for them is 4 billion wide all the predefined names are in the
> range < 100 and separated by only 10 so it's tricky to wedge things
> between the existing names.

Maybe we need a RENUM script? :)



-adrian

>
> The strangest bit is when you have interdependent drivers at different
> early pass numbers.  Sometimes it's necessary to do almost nothing in
> the attach() routine and do all the real attach-time type stuff in a
> bus_new_pass() routine after the pass number becomes high enough that
> your co-dependent driver peers are available.
>
> -- Ian
>
>
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