From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7940BECAAA1 for ; Sun, 30 Oct 2022 16:16:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229610AbiJ3QNM (ORCPT ); Sun, 30 Oct 2022 12:13:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34654 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229494AbiJ3QNK (ORCPT ); Sun, 30 Oct 2022 12:13:10 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0FC6B5FB6 for ; Sun, 30 Oct 2022 09:13:09 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 8F33560EE0 for ; Sun, 30 Oct 2022 16:13:08 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 74CABC433C1; Sun, 30 Oct 2022 16:13:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1667146387; bh=/T3JSPF6RKm+uD0J6i/rJY8j22suaEB2nqLWyc8WVfQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=obSU/JkGAzLXB2CTMQPpINuXYLeHg6YL1DjxNB2QF7uMKz1r/E7SidAZAcS1fpMpx Yw4PyaS2BTlkZXWZh+cZULssGS8MF+Ih3xf1QgmjQm0/fusis7NSu/If3paWkdmn5Z Lece3ClpVkyI3+sO6OHjYr7XANVbCpYCaJFtPJNf7ugSIDVX/mzmQnNd0BOqtEG8V+ RaxjnyR/Q44cJS+D92wTN7fXCb+/KiTnETa3m2SIrALQmnDEqJ3qLY8C7S6sIXeLCN mODLW7ndGAZLTJbb6yPA+rJ7V9awtGeVDa3Z7AI7OY2bhSikKU7mfV9WAXwaYYfbVo aAMcc9GXrupKQ== Date: Mon, 31 Oct 2022 00:03:20 +0800 From: Jisheng Zhang To: Andrew Jones Cc: Paul Walmsley , Palmer Dabbelt , Albert Ou , linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 0/8] riscv: improve boot time isa extensions handling Message-ID: References: <20221006070818.3616-1-jszhang@kernel.org> <20221029095609.e4ymkbnk2hl3kxzc@kamzik> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20221029095609.e4ymkbnk2hl3kxzc@kamzik> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Oct 29, 2022 at 11:56:09AM +0200, Andrew Jones wrote: > On Thu, Oct 06, 2022 at 03:08:10PM +0800, Jisheng Zhang wrote: > > Generally, riscv ISA extensions are fixed for any specific hardware > > platform, that's to say, the hart features won't change any more > > after booting, this chacteristic make it straightforward to use > > static branch to check one specific ISA extension is supported or not > > to optimize performance. > > > > However, some ISA extensions such as SVPBMT and ZICBOM are handled > > via. the alternative sequences. > > > > Basically, for ease of maintenance, we prefer to use static branches > > in C code, but recently, Samuel found that the static branch usage in > > cpu_relax() breaks building with CONFIG_CC_OPTIMIZE_FOR_SIZE[1]. As > > Samuel pointed out, "Having a static branch in cpu_relax() is > > problematic because that function is widely inlined, including in some > > quite complex functions like in the VDSO. A quick measurement shows > > this static branch is responsible by itself for around 40% of the jump > > table." > > > > Samuel's findings pointed out one of a few downsides of static branches > > usage in C code to handle ISA extensions detected at boot time: > > static branch's metadata in the __jump_table section, which is not > > discarded after ISA extensions are finalized, wastes some space. > > > > I want to try to solve the issue for all possible dynamic handling of > > ISA extensions at boot time. Inspired by Mark[2], this patch introduces > > riscv_has_extension_*() helpers, which work like static branches but > > are patched using alternatives, thus the metadata can be freed after > > patching. > > > > [1]https://lore.kernel.org/linux-riscv/20220922060958.44203-1-samuel@sholland.org/ > > [2]https://lore.kernel.org/linux-arm-kernel/20220912162210.3626215-8-mark.rutland@arm.com/ > > > > > > Jisheng Zhang (8): > > riscv: move riscv_noncoherent_supported() out of ZICBOM probe > > riscv: cpufeature: detect RISCV_ALTERNATIVES_EARLY_BOOT earlier > > riscv: hwcap: make ISA extension ids can be used in asm > > riscv: cpufeature: extend riscv_cpufeature_patch_func to all ISA > > extensions > > riscv: introduce riscv_has_extension_[un]likely() > > riscv: fpu: switch has_fpu() to riscv_has_extension_likely() > > riscv: cpu_relax: switch to riscv_has_extension_likely() > > riscv: remove riscv_isa_ext_keys[] array and related usage > > > > arch/riscv/include/asm/errata_list.h | 9 +-- > > arch/riscv/include/asm/hwcap.h | 94 ++++++++++++++----------- > > arch/riscv/include/asm/switch_to.h | 3 +- > > arch/riscv/include/asm/vdso/processor.h | 2 +- > > arch/riscv/kernel/cpufeature.c | 78 +++----------------- > > arch/riscv/kernel/setup.c | 4 ++ > > 6 files changed, 71 insertions(+), 119 deletions(-) > > > > -- > > 2.37.2 > > > > Hi Jisheng, > > I just tried building this with LLVM=1 and fails to compile with messages > like > > ld.lld: error: relocation R_RISCV_64 cannot be used against symbol '.Ltmp1'; recompile with -fPIC > >>> defined in arch/riscv/kernel/vdso/vgettimeofday.o > >>> referenced by vgettimeofday.c > >>> arch/riscv/kernel/vdso/vgettimeofday.o:(.alternative+0x0) > > It does compile and boot with CC=clang and binutils 2.39, where my clang > version is 14.0.5 (Fedora 14.0.5-1.fc36). Hi Andrew, Below is a quick fix. PS: I think I need add two or more patches to apply alternatives in the vDSO. But currently only Zihintpause is affected. Will send out a new version. diff --git a/arch/riscv/kernel/vdso/Makefile b/arch/riscv/kernel/vdso/Makefile index f2e065671e4d..522b78477bab 100644 --- a/arch/riscv/kernel/vdso/Makefile +++ b/arch/riscv/kernel/vdso/Makefile @@ -44,7 +44,7 @@ $(obj)/vdso.o: $(obj)/vdso.so # link rule for the .so file, .lds has to be first $(obj)/vdso.so.dbg: $(obj)/vdso.lds $(obj-vdso) FORCE $(call if_changed,vdsold) -LDFLAGS_vdso.so.dbg = -shared -S -soname=linux-vdso.so.1 \ +LDFLAGS_vdso.so.dbg = -shared -z notext -S -soname=linux-vdso.so.1 \ > > Thanks, > drew