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 mm01.cs.columbia.edu (mm01.cs.columbia.edu [128.59.11.253]) by smtp.lore.kernel.org (Postfix) with ESMTP id E668BC433F5 for ; Wed, 20 Apr 2022 17:44:15 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 845424B0FB; Wed, 20 Apr 2022 13:44:15 -0400 (EDT) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id S585OZi7HR40; Wed, 20 Apr 2022 13:44:11 -0400 (EDT) Received: from mm01.cs.columbia.edu (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 77A094B17D; Wed, 20 Apr 2022 13:44:11 -0400 (EDT) Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id B51E84B10C for ; Wed, 20 Apr 2022 13:44:09 -0400 (EDT) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id yzOoEW4rgqgY for ; Wed, 20 Apr 2022 13:44:08 -0400 (EDT) Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by mm01.cs.columbia.edu (Postfix) with ESMTPS id 77DA34B0FB for ; Wed, 20 Apr 2022 13:44:08 -0400 (EDT) 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 ams.source.kernel.org (Postfix) with ESMTPS id CC6FAB81EB6; Wed, 20 Apr 2022 17:44:06 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 797EBC385A0; Wed, 20 Apr 2022 17:44:03 +0000 (UTC) Date: Wed, 20 Apr 2022 18:44:00 +0100 From: Catalin Marinas To: Marc Zyngier Subject: Re: [PATCH v2 10/10] arm64: Use WFxT for __delay() when possible Message-ID: References: <20220419182755.601427-1-maz@kernel.org> <20220419182755.601427-11-maz@kernel.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20220419182755.601427-11-maz@kernel.org> Cc: kernel-team@android.com, kvm@vger.kernel.org, Joey Gouly , Will Deacon , kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org X-BeenThere: kvmarm@lists.cs.columbia.edu X-Mailman-Version: 2.1.14 Precedence: list List-Id: Where KVM/ARM decisions are made List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu On Tue, Apr 19, 2022 at 07:27:55PM +0100, Marc Zyngier wrote: > Marginally optimise __delay() by using a WFIT/WFET sequence. > It probably is a win if no interrupt fires during the delay. > > Signed-off-by: Marc Zyngier > --- > arch/arm64/lib/delay.c | 12 +++++++++++- > 1 file changed, 11 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/lib/delay.c b/arch/arm64/lib/delay.c > index 1688af0a4c97..5b7890139bc2 100644 > --- a/arch/arm64/lib/delay.c > +++ b/arch/arm64/lib/delay.c > @@ -27,7 +27,17 @@ void __delay(unsigned long cycles) > { > cycles_t start = get_cycles(); > > - if (arch_timer_evtstrm_available()) { > + if (cpus_have_const_cap(ARM64_HAS_WFXT)) { > + u64 end = start + cycles; > + > + /* > + * Start with WFIT. If an interrupt makes us resume > + * early, use a WFET loop to complete the delay. > + */ > + wfit(end); > + while ((get_cycles() - start) < cycles) > + wfet(end); Do you use WFET here as a pending interrupt would cause WFIT to complete immediately? > + } else if (arch_timer_evtstrm_available()) { Nit: two spaces between else and if ;). Acked-by: Catalin Marinas _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm