Date: Sat, 4 May 2019 00:03:50 -0700 From: Mark Millard <marklmi@yahoo.com> To: Justin Hibbits <chmeeedalf@gmail.com>, FreeBSD PowerPC ML <freebsd-ppc@freebsd.org> Subject: Re: The first 2 handle_kernel_slb_spill calls on the 2-socket/2-cores-each G5 example context: as expected? (short) Message-ID: <47414D54-99F2-490C-AFFC-43503556FA4A@yahoo.com> In-Reply-To: <2388C664-2D47-4851-95AF-A125CE48C282@yahoo.com> References: <9D9A51A9-C8A6-475F-B241-0A3C3546D3D6.ref@yahoo.com> <9D9A51A9-C8A6-475F-B241-0A3C3546D3D6@yahoo.com> <2388C664-2D47-4851-95AF-A125CE48C282@yahoo.com>
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[I forgot to show where I always stop the enable of the
reporting.]
On 2019-May-3, at 23:52, Mark Millard <marklmi at yahoo.com> wrote:
> [A correction --and interesting information from a somewhat later
> time frame.]
>=20
> On 2019-May-3, at 20:22, Mark Millard <marklmi at yahoo.com> wrote:
>=20
>> [This is from the -r347003 experiment context, not my
>> normal environment.]
>>=20
>> I stuck a printf in handle_kernel_slb_spill, reporting the type,
>> dar, and srr0 values. The resultant build does not get far
>> booting but does report the first 2 calls. Typed from a screen
>> picture:
>>=20
>> KDB: debugger backends: ddb
>> KDB: current backend: ddb
>> handle_kernel_slb_spill: type=3D0x380 dar=3D0x3d99348 srr0=3D0xa869bc
>> handle_kernel_slb_spill: type=3D0x380 dar=3D0x10000000 srr0=3D0xa869bc
>>=20
>> That is as far as it gets, as far as output goes, with that
>> unconditional printf in place.
>>=20
>> (I was not sure I'd get anything from this experiment.)
>>=20
>> This suggests that the slb is partially(?) populated in the
>> hardware before the (adjusted) loop that I've been testing with
>> tries to establish coverage of part of the KVA space. The two
>> examples reported are from neither the Direct-Map space nor the
>> Kernel-Virtual-Address space.
>>=20
>> Are these expected? Is their presence handled?
>>=20
>=20
> I made the printf in handle_kernel_slb_spill conditional
> on a global so I could control when it would try to
> print.
>=20
> I learned that I guessed the ordering wrong on the initial
> report:
>=20
> QUOTE
> #ifdef __powerpc64__
> i =3D 0;
> for (va =3D virtual_avail; va < virtual_end && i<(n_slbs-1)/2; =
va +=3D SEGMENT_LENGTH, i++)
> moea64_bootstrap_slb_prefault(va, 0);
> #endif
> enable_handle_kernel_slb_spill_reporting=3D 1;
> END QUOTE
>=20
> gets the lines I originally showed:
>=20
> handle_kernel_slb_spill: type=3D0x380 dar=3D0x3d99348 srr0=3D0xa869bc
> handle_kernel_slb_spill: type=3D0x380 dar=3D0x10000000 srr0=3D0xa869bc
>=20
> So these were after then loop, not before.
>=20
> Note: So far those messages always have displayed and
> then things were hung-up for this enable placement.
>=20
>=20
> I then commented that enable out and added a
> printf:
>=20
> pa =3D moea64_bootstrap_alloc(kstack_pages * PAGE_SIZE, =
PAGE_SIZE);
> va =3D virtual_avail + KSTACK_GUARD_PAGES * PAGE_SIZE;
> virtual_avail =3D va + kstack_pages * PAGE_SIZE;
> CTR2(KTR_PMAP, "moea64_bootstrap: kstack0 at %#x (%#x)", pa, =
va);
> printf("moea64_bootstrap: kstack0 at %#x (%#x)\n", pa, va);
>=20
> and also set up an enable just before dpcpu_init's=20
> all:
>=20
> enable_handle_kernel_slb_spill_reporting=3D 1;
> dpcpu_init(dpcpu, curcpu);
>=20
> The result, when it did not boot, was as below,
> again showing a couple of handle_kernel_slb_spill
> lines for a not very large addresses and no more
> lines after that:
>=20
> KDB: debugger backends: ddb
> KDB: current backend: ddb
> moea64_bootstrap: kstack0 at 0x3000 (0x1000)
> handle_kernel_slb_spill: type=3D0x380 dar=3D0x22ef8 srr0=3D0xa86690
> handle_kernel_slb_spill: type=3D0x480 dar=3D0x22ef8 srr0=3D0xa86690
>=20
> It is the same addresses but two distinct types. It
> also would seem to be the same segment as for:
>=20
> handle_kernel_slb_spill: type=3D0x380 dar=3D0x3d99348 srr0=3D0xa869bc
> (from the earlier placement)
>=20
>=20
> By contrast, interestingly, it did sometimes boot for
> this later enable placement, and, when it did boot,
> there were no handle_kernel_slb_spill lines output:
>=20
> KDB: debugger backends: ddb
> KDB: current backend: ddb
> moea64_bootstrap: kstack0 at 0x3000 (0x1000)
> ---<<BOOT>>---
>=20
> (and so on.)
>=20
>=20
> This means that the type=3D0x?80 dar=3D0x22ef8 srr0=3D0xa86690
> slb-misses are intermittent for this testing context.
>=20
>=20
> Of course, with more testing I might see more variability.
I forgot to show that I used:
/* Bring up virtual memory */
moea64_late_bootstrap(mmup, kernelstart, kernelend);
enable_handle_kernel_slb_spill_reporting=3D 0; // hangs without printf =
display first when this late
}
It did no good the enable it this late so I set
it as a disable point instead. Trying to use the
handle_kernel_slb_spill printf after this point
seem to just result in silently hanging-up.
So this disable was involved in the cases that
booted for enabling just before dpcpu_init .
(It is not clear just how far the non-booting
cases got internally.)
=3D=3D=3D
Mark Millard
marklmi at yahoo.com
( dsl-only.net went
away in early 2018-Mar)
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