From: "Heiko Stübner" <heiko@sntech.de>
To: Paul Walmsley <paul.walmsley@sifive.com>,
Palmer Dabbelt <palmer@dabbelt.com>,
Albert Ou <aou@eecs.berkeley.edu>,
Anup Patel <anup@brainfault.org>,
Atish Patra <atishp@atishpatra.org>,
Jisheng Zhang <jszhang@kernel.org>
Cc: linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
kvm@vger.kernel.org, kvm-riscv@lists.infradead.org,
Andrew Jones <ajones@ventanamicro.com>
Subject: Re: [PATCH v3 05/13] riscv: cpufeature: extend riscv_cpufeature_patch_func to all ISA extensions
Date: Thu, 12 Jan 2023 00:29:57 +0100 [thread overview]
Message-ID: <2398293.3Lj2Plt8kZ@diego> (raw)
In-Reply-To: <20230111171027.2392-6-jszhang@kernel.org>
Hi Jisheng.
Am Mittwoch, 11. Januar 2023, 18:10:19 CET schrieb Jisheng Zhang:
> riscv_cpufeature_patch_func() currently only scans a limited set of
> cpufeatures, explicitly defined with macros. Extend it to probe for all
> ISA extensions.
>
> Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
> Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
> Reviewed-by: Heiko Stuebner <heiko@sntech.de>
> ---
> arch/riscv/include/asm/errata_list.h | 9 ++--
> arch/riscv/kernel/cpufeature.c | 63 ++++------------------------
> 2 files changed, 11 insertions(+), 61 deletions(-)
hmmm ... I do see a somewhat big caveat for this.
and would like to take back my Reviewed-by for now
With this change we would limit the patchable cpufeatures to actual
riscv extensions. But cpufeatures can also be soft features like
how performant the core handles unaligned accesses.
See Palmer's series [0].
Also this essentially codifies that each ALTERNATIVE can only ever
be attached to exactly one extension.
But contrary to vendor-errata, it is very likely that we will need
combinations of different extensions for some alternatives in the future.
In my optimization quest, I found that it's actually pretty neat to
convert the errata-id for cpufeatures to a bitfield [1], because then it's
possible to just combine extensions into said bitfield [2]:
ALTERNATIVE_2("nop",
"j strcmp_zbb_unaligned", 0, CPUFEATURE_ZBB | CPUFEATURE_FAST_UNALIGNED, 0, CONFIG_RISCV_ISA_ZBB,
"j variant_zbb", 0, CPUFEATURE_ZBB, CPUFEATURE_FAST_UNALIGNED, CONFIG_RISCV_ISA_ZBB)
[the additional field there models a "not" component]
So I really feel this would limit us quite a bit.
Heiko
[0] https://git.kernel.org/pub/scm/linux/kernel/git/palmer/linux.git/commit/?h=riscv-hwprobe-v1&id=510c491cb9d87dcbdc91c63558dc704968723240
[1] https://github.com/mmind/linux-riscv/commit/f57a896122ee7e666692079320fc35829434cf96
[2] https://github.com/mmind/linux-riscv/commit/8cef615dab0c00ad68af2651ee5b93d06be17f27#diff-194cb8a86f9fb9b03683295f21c8f46b456a9f94737f01726ddbcbb9e3aace2cR12
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next prev parent reply other threads:[~2023-01-11 23:30 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-11 17:10 [PATCH v3 00/13] riscv: improve boot time isa extensions handling Jisheng Zhang
2023-01-11 17:10 ` [PATCH v3 01/13] riscv: fix jal offsets in patched alternatives Jisheng Zhang
2023-01-11 17:56 ` Andrew Jones
2023-01-11 23:31 ` Heiko Stübner
2023-01-12 20:25 ` Conor Dooley
2023-01-11 17:10 ` [PATCH v3 02/13] riscv: move riscv_noncoherent_supported() out of ZICBOM probe Jisheng Zhang
2023-01-11 17:10 ` [PATCH v3 03/13] riscv: cpufeature: detect RISCV_ALTERNATIVES_EARLY_BOOT earlier Jisheng Zhang
2023-01-12 21:11 ` Conor Dooley
2023-01-11 17:10 ` [PATCH v3 04/13] riscv: hwcap: make ISA extension ids can be used in asm Jisheng Zhang
2023-01-12 21:28 ` Conor Dooley
2023-01-15 13:13 ` Jisheng Zhang
2023-01-11 17:10 ` [PATCH v3 05/13] riscv: cpufeature: extend riscv_cpufeature_patch_func to all ISA extensions Jisheng Zhang
2023-01-11 23:29 ` Heiko Stübner [this message]
2023-01-12 9:21 ` Andrew Jones
2023-01-13 15:18 ` Conor Dooley
2023-01-14 20:32 ` Conor Dooley
2023-01-18 21:54 ` Conor Dooley
2023-01-19 8:29 ` Andrew Jones
2023-01-19 22:13 ` Conor Dooley
2023-01-15 13:59 ` Jisheng Zhang
2023-01-15 14:19 ` Jisheng Zhang
2023-01-11 17:10 ` [PATCH v3 06/13] riscv: introduce riscv_has_extension_[un]likely() Jisheng Zhang
2023-01-11 17:10 ` [PATCH v3 07/13] riscv: fpu: switch has_fpu() to riscv_has_extension_likely() Jisheng Zhang
2023-01-12 21:58 ` Conor Dooley
2023-01-11 17:10 ` [PATCH v3 08/13] riscv: module: move find_section to module.h Jisheng Zhang
2023-01-11 17:10 ` [PATCH v3 09/13] riscv: switch to relative alternative entries Jisheng Zhang
2023-01-11 18:11 ` Andrew Jones
2023-01-12 21:49 ` Conor Dooley
2023-01-11 17:10 ` [PATCH v3 10/13] riscv: alternative: patch alternatives in the vDSO Jisheng Zhang
2023-01-11 23:55 ` kernel test robot
2023-01-12 7:48 ` Conor Dooley
2023-01-12 21:55 ` Conor Dooley
2023-01-11 17:10 ` [PATCH v3 11/13] riscv: cpu_relax: switch to riscv_has_extension_likely() Jisheng Zhang
2023-01-12 21:59 ` Conor Dooley
2023-01-11 17:10 ` [PATCH v3 12/13] riscv: KVM: Switch has_svinval() to riscv_has_extension_unlikely() Jisheng Zhang
2023-01-11 17:10 ` [PATCH v3 13/13] riscv: remove riscv_isa_ext_keys[] array and related usage Jisheng Zhang
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