From patchwork Tue Oct 10 10:31:25 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mark Rutland X-Patchwork-Id: 13415157 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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 65714CD80A1 for ; Tue, 10 Oct 2023 10:33:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Message-Id:Date:Subject:Cc:To:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=XKjNSactFrgMjBRkQEbElUTBalm/jcTjH3oGZcBJfr0=; b=MgzW3LB/OLohX0 9YcM+Aj/aTHRKuMe16yasz2xnZ+rbnGWFJZ6RAZZHHIG+mH+u5Bug2kNb6eXq82J60hH3NaFDXsQ1 GJ8nTtb4zPHP2Kr2Zfg/kW2mxqtolOAIIauMH4k5UD718fabh+xun5Ioe60Qbf5GZNu1VJdCv7ytY RVZv+vG/J+FzyDECpb3OWgfVUqnm5pLkQ7X44smtNtu3WkDJ3/JKC/2oxbi37Rc9wVzxVZcASOC4E xRft5JOSUGzqU32TnSw8M7BC//0VQN70pbGRTuygvGFYa2kOye6cis6eYtjQnZKzzE11LvcxCu9LZ 7zgjb7XcN4mWTZS7d7Ow==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1qqA3E-00D2k0-2j; Tue, 10 Oct 2023 10:33:20 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1qqA2o-00D2Mv-0y for linux-arm-kernel@lists.infradead.org; Tue, 10 Oct 2023 10:32:58 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 2F28A1FB; Tue, 10 Oct 2023 03:33:34 -0700 (PDT) Received: from lakrids.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 2DE403F762; Tue, 10 Oct 2023 03:32:51 -0700 (PDT) From: Mark Rutland To: linux-arm-kernel@lists.infradead.org Cc: ardb@kernel.org, bertrand.marquis@arm.com, boris.ostrovsky@oracle.com, broonie@kernel.org, catalin.marinas@arm.com, daniel.lezcano@linaro.org, james.morse@arm.com, jgross@suse.com, kristina.martsenko@arm.com, mark.rutland@arm.com, maz@kernel.org, oliver.upton@linux.dev, pcc@google.com, sstabellini@kernel.org, suzuki.poulose@arm.com, tglx@linutronix.de, vladimir.murzin@arm.com, will@kernel.org Subject: [PATCH v3 24/38] arm64: Avoid cpus_have_const_cap() for ARM64_HAS_WFXT Date: Tue, 10 Oct 2023 11:31:25 +0100 Message-Id: <20231010103139.3113421-25-mark.rutland@arm.com> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20231010103139.3113421-1-mark.rutland@arm.com> References: <20231010103139.3113421-1-mark.rutland@arm.com> MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20231010_033254_450922_DF954713 X-CRM114-Status: GOOD ( 17.04 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org In __delay() we use cpus_have_const_cap() to check for ARM64_HAS_WFXT, but this is not necessary and alternative_has_cap() would be preferable. For historical reasons, cpus_have_const_cap() is more complicated than it needs to be. Before cpucaps are finalized, it will perform a bitmap test of the system_cpucaps bitmap, and once cpucaps are finalized it will use an alternative branch. This used to be necessary to handle some race conditions in the window between cpucap detection and the subsequent patching of alternatives and static branches, where different branches could be out-of-sync with one another (or w.r.t. alternative sequences). Now that we use alternative branches instead of static branches, these are all patched atomically w.r.t. one another, and there are only a handful of cases that need special care in the window between cpucap detection and alternative patching. Due to the above, it would be nice to remove cpus_have_const_cap(), and migrate callers over to alternative_has_cap_*(), cpus_have_final_cap(), or cpus_have_cap() depending on when their requirements. This will remove redundant instructions and improve code generation, and will make it easier to determine how each callsite will behave before, during, and after alternative patching. The cpus_have_const_cap() check in __delay() is an optimization to use WFIT and WFET in preference to busy-polling the counter and/or using regular WFE and relying upon the architected timer event stream. It is not necessary to apply this optimization in the window between detecting the ARM64_HAS_WFXT cpucap and patching alternatives. This patch replaces the use of cpus_have_const_cap() with alternative_has_cap_unlikely(), which will avoid generating code to test the system_cpucaps bitmap and should be better for all subsequent calls at runtime. Signed-off-by: Mark Rutland Cc: Catalin Marinas Cc: Marc Zyngier Cc: Suzuki K Poulose Cc: Will Deacon --- arch/arm64/lib/delay.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/arm64/lib/delay.c b/arch/arm64/lib/delay.c index 5b7890139bc2f..cb2062e7e2340 100644 --- a/arch/arm64/lib/delay.c +++ b/arch/arm64/lib/delay.c @@ -27,7 +27,7 @@ void __delay(unsigned long cycles) { cycles_t start = get_cycles(); - if (cpus_have_const_cap(ARM64_HAS_WFXT)) { + if (alternative_has_cap_unlikely(ARM64_HAS_WFXT)) { u64 end = start + cycles; /*