linux-kernel - Re: [PATCH 00/14] Reduce alignment constraint on STRICT_KERNEL_RWX and speed-up TLB misses on 8xx and 603

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Message-Id: <172562357202.467568.4096138067751916114.b4-ty@ellerman.id.au>
Date: Fri, 06 Sep 2024 21:52:52 +1000
From: Michael Ellerman <patch-notifications@...erman.id.au>
To: CASAUBON Jean Michel <jean-michel.casaubon@...soprasteria.com>, Michael Ellerman <mpe@...erman.id.au>, Nicholas Piggin <npiggin@...il.com>, Naveen N Rao <naveen@...nel.org>, Christophe Leroy <christophe.leroy@...roup.eu>
Cc: linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH 00/14] Reduce alignment constraint on STRICT_KERNEL_RWX and speed-up TLB misses on 8xx and 603

On Tue, 20 Aug 2024 19:23:44 +0200, Christophe Leroy wrote:
> This series does mainly two things:
> - Remove the 8M alignment constraint on STRICT_KERNEL_RWX on 8xx to
> avoid wasting memory.
> - Speed-up TLB misses by duplicating kernel PGD entries into each
> task's PGDIRs to avoid the address comparison in TLB miss handler.
> 
> On 8xx, the address comparison takes a significant part of CPU cycles
> as it requires saving/restoring CR, and because a taken branch
> requires 2 cycles.
> On 603 it is less significant because CR is saved automatically and
> has to be restored anyway but it is still worth it.
> 
> [...]

Applied to powerpc/next.

[01/14] powerpc/8xx: Fix initial memory mapping
        https://git.kernel.org/powerpc/c/f9f2bff64c2f0dbee57be3d8c2741357ad3d05e6
[02/14] powerpc/8xx: Fix kernel vs user address comparison
        https://git.kernel.org/powerpc/c/65a82e117ffeeab0baf6f871a1cab11a28ace183
[03/14] powerpc/8xx: Copy kernel PGD entries into all PGDIRs
        https://git.kernel.org/powerpc/c/985db026c34dfc45213649023d5505822a5dcd78
[04/14] Revert "powerpc/8xx: Always pin kernel text TLB"
        https://git.kernel.org/powerpc/c/1a736d98c84acd38e40fff69528ce7aaa55dd22d
[05/14] powerpc/8xx: Allow setting DATA alignment even with STRICT_KERNEL_RWX
        https://git.kernel.org/powerpc/c/bcf77a70c4ffc9b01044229de87f5b6f9c1f7913
[06/14] powerpc/8xx: Reduce default size of module/execmem area
        https://git.kernel.org/powerpc/c/c5eec4df25c34f4bee8c757ed157f5d96eaba554
[07/14] powerpc/8xx: Preallocate execmem page tables
        https://git.kernel.org/powerpc/c/16a71c045186a11c1c743934e330de78162b86dd
[08/14] powerpc/8xx: Inconditionally use task PGDIR in ITLB misses
        https://git.kernel.org/powerpc/c/33c527522f394f63cc589a6f7af990b2232444c8
[09/14] powerpc/8xx: Inconditionally use task PGDIR in DTLB misses
        https://git.kernel.org/powerpc/c/ac9f97ff8b324905d457f2694490c63b9deccbc6
[10/14] powerpc/32s: Reduce default size of module/execmem area
        https://git.kernel.org/powerpc/c/2f2b9a3adc66e978a1248ffb38df8477e8e97c57
[11/14] powerpc/603: Copy kernel PGD entries into all PGDIRs and preallocate execmem page tables
        https://git.kernel.org/powerpc/c/82ef440f9a38a1fd7f4854397633a35af33840a5
[12/14] powerpc/603: Switch r0 and r3 in TLB miss handlers
        https://git.kernel.org/powerpc/c/31c0e137ec609f36877ea39cd343ef2476d080aa
[13/14] powerpc/603: Inconditionally use task PGDIR in ITLB misses
        https://git.kernel.org/powerpc/c/3f57d90c231d3329aaed7079dd05b5a2f7692a58
[14/14] powerpc/603: Inconditionally use task PGDIR in DTLB misses
        https://git.kernel.org/powerpc/c/062e825a336017c0334c7497690826c95aa1a84f

cheers