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 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 73556D44D55 for ; Wed, 6 Nov 2024 11:58:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=58kGrfeVq2CuCcd99sNgGdxG4moqweOY1MYVaFoTru8=; b=XEoIQH+vkK7kuTK8CL7YS+HQRC a7FglJJNRyUVRtjRF9fxXPK30xq5T8ZJ84ZE1+4yORO0uDzJOrgB9LriypLeN6vZJwr+OZrS993Wo Yy7Pw379tnXqx/q8g0AVdGwPiUCtMQQVOGaAsbgVnBMoEq3SF60XpoqXFPADpM3Qspyk5qCGe7kVK ApkiqpgbwnBpYmMeXThDnWils0Ib7TT2gn+/ipFs0UCtXDRENrOKbVhrpHcPtTMgueQOckGa0u5oE dLSvulQFpU5eUNPPaarq8+IDq5/R5c258C6CZeH7IFdfQrLMpuBH4DtObBOLvp/k5wdZ0ka3Tv0V3 ZzXz2aFw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1t8eff-000000033Xf-2Mou; Wed, 06 Nov 2024 11:57:59 +0000 Received: from dfw.source.kernel.org ([2604:1380:4641:c500::1]) by bombadil.infradead.org with esmtps (Exim 4.98 #2 (Red Hat Linux)) id 1t8dtf-00000002sNM-3wlq for linux-arm-kernel@lists.infradead.org; Wed, 06 Nov 2024 11:08:25 +0000 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by dfw.source.kernel.org (Postfix) with ESMTP id 7859A5C585B; Wed, 6 Nov 2024 11:07:38 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 147B3C4CECD; Wed, 6 Nov 2024 11:08:17 +0000 (UTC) Date: Wed, 6 Nov 2024 11:08:15 +0000 From: Catalin Marinas To: Haris Okanovic Cc: ankur.a.arora@oracle.com, linux-pm@vger.kernel.org, kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, will@kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, pbonzini@redhat.com, wanpengli@tencent.com, vkuznets@redhat.com, rafael@kernel.org, daniel.lezcano@linaro.org, peterz@infradead.org, arnd@arndb.de, lenb@kernel.org, mark.rutland@arm.com, mtosatti@redhat.com, sudeep.holla@arm.com, cl@gentwo.org, misono.tomohiro@fujitsu.com, maobibo@loongson.cn, joao.m.martins@oracle.com, boris.ostrovsky@oracle.com, konrad.wilk@oracle.com Subject: Re: [PATCH 1/5] asm-generic: add smp_vcond_load_relaxed() Message-ID: References: <20240925232425.2763385-1-ankur.a.arora@oracle.com> <20241105183041.1531976-1-harisokn@amazon.com> <20241105183041.1531976-2-harisokn@amazon.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20241105183041.1531976-2-harisokn@amazon.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20241106_030824_130878_578E2D83 X-CRM114-Status: GOOD ( 17.65 ) 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 On Tue, Nov 05, 2024 at 12:30:37PM -0600, Haris Okanovic wrote: > diff --git a/include/asm-generic/barrier.h b/include/asm-generic/barrier.h > index d4f581c1e21d..112027eabbfc 100644 > --- a/include/asm-generic/barrier.h > +++ b/include/asm-generic/barrier.h > @@ -256,6 +256,31 @@ do { \ > }) > #endif > > +/** > + * smp_vcond_load_relaxed() - (Spin) wait until an expected value at address > + * with no ordering guarantees. Spins until `(*addr & mask) == val` or > + * `nsecs` elapse, and returns the last observed `*addr` value. > + * > + * @nsecs: timeout in nanoseconds FWIW, I don't mind the relative timeout, it makes the API easier to use. Yes, it may take longer in absolute time if the thread is scheduled out before local_clock_noinstr() is read but the same can happen in the caller anyway. It's similar to udelay(), it can take longer if the thread is scheduled out. > + * @addr: pointer to an integer > + * @mask: a bit mask applied to read values > + * @val: Expected value with mask > + */ > +#ifndef smp_vcond_load_relaxed > +#define smp_vcond_load_relaxed(nsecs, addr, mask, val) ({ \ > + const u64 __start = local_clock_noinstr(); \ > + u64 __nsecs = (nsecs); \ > + typeof(addr) __addr = (addr); \ > + typeof(*__addr) __mask = (mask); \ > + typeof(*__addr) __val = (val); \ > + typeof(*__addr) __cur; \ > + smp_cond_load_relaxed(__addr, ( \ > + (VAL & __mask) == __val || \ > + local_clock_noinstr() - __start > __nsecs \ > + )); \ > +}) The generic implementation has the same problem as Ankur's current series. smp_cond_load_relaxed() can't wait on anything other than the variable at __addr. If it goes into a WFE, there's nothing executed to read the timer and check for progress. Any generic implementation of such function would have to use cpu_relax() and polling. -- Catalin