From: Segher Boessenkool <segher@kernel.crashing.org>
To: Michael Ellerman <mpe@ellerman.id.au>
Cc: linuxppc-dev@ozlabs.org, npiggin@gmail.com
Subject: Re: [PATCH 2/4] powerpc/64s: Add slb_full_bitmap rather than hard-coding U32_MAX
Date: Fri, 18 Jan 2019 17:12:43 -0600 [thread overview]
Message-ID: <20190118231243.GV14180@gate.crashing.org> (raw)
In-Reply-To: <87ef9a40bb.fsf@concordia.ellerman.id.au>
On Fri, Jan 18, 2019 at 11:28:24PM +1100, Michael Ellerman wrote:
> Segher Boessenkool <segher@kernel.crashing.org> writes:
>
> > On Thu, Jan 17, 2019 at 11:13:26PM +1100, Michael Ellerman wrote:
> >> The recent rewrite of the SLB code into C included the assumption that
> >> all CPUs we run on have at least 32 SLB entries. This is currently
> >> true but a bit fragile as the SLB size is actually defined by the
> >> device tree and so could theoretically change at any time.
> >
> > It also is guaranteed by the architecture, since at least 2.02, FWIW.
>
> True. Actually 2.00 says at least 32.
>
> Unfortunately we don't live in a world where "the architecture
> guarantees it" has any bearing on reality :)
It's a pretty strong hint. I don't remember any hardware where it is not
true, either. (That might be selective memory ;-) )
> But given it *should* always be at least 32 maybe I should optimise for
> that case. We could use a static key to skip the U32_MAX comparison and
> go down the else path.
Ah that sounds like a good idea :-)
Segher
next prev parent reply other threads:[~2019-01-18 23:14 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-17 12:13 [PATCH 1/4] powerpc/64s: Always set mmu_slb_size using slb_set_size() Michael Ellerman
2019-01-17 12:13 ` [PATCH 2/4] powerpc/64s: Add slb_full_bitmap rather than hard-coding U32_MAX Michael Ellerman
2019-01-17 16:30 ` Segher Boessenkool
2019-01-18 12:28 ` Michael Ellerman
2019-01-18 23:12 ` Segher Boessenkool [this message]
2019-01-23 9:02 ` Aneesh Kumar K.V
2019-01-17 12:13 ` [PATCH 3/4] powerpc/64s: Move SLB init into hash_utils_64.c Michael Ellerman
2019-01-23 9:04 ` Aneesh Kumar K.V
2019-01-17 12:13 ` [PATCH 4/4] powerpc/64s: Support shrinking the SLB for debugging Michael Ellerman
2019-01-19 0:13 ` Michal Suchánek
2019-01-19 10:27 ` Michael Ellerman
2019-01-23 8:40 ` Nicholas Piggin
2019-01-23 9:10 ` Aneesh Kumar K.V
2019-01-23 8:59 ` [PATCH 1/4] powerpc/64s: Always set mmu_slb_size using slb_set_size() Aneesh Kumar K.V
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