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 79967C433F5 for ; Thu, 17 Mar 2022 18:04:30 +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-Type: Content-Transfer-Encoding:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:From:References:Cc:To:Subject: MIME-Version:Date:Message-ID:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=gOIeA9pknMJZQF9WyxnrJCT1KuDdq87BfRDxXaNx6O0=; b=jgqCgMGaKqjEUZ hQ7BNIr2zgG3rlues5BRjmjEDt9eakXL5pN47FPH5IJrz6Ol0RZhvogboyY4MBh1y0FIhcpRXUKSo uTjaGJWbV6pVKR98ZBDqrZpbmDbW1lj6gKvMIFwW7ym4cHeWUIloPZ5RT80C3+KYNhfSX3v6I91WG qfvF+nJNEv7doI8BByQD2GWSzxwmcYz5f/GFGdBGuwbHl2y67j87v9sYvE/GIochT0GuZd5HPDxSH YkvvmVyfKORG8GCWEHtUpr0Ia1WJlFonxsecIjcbE9OUyPReMYFiZNxGRAcONbDXYsT8oUDwolmG/ ZUtHXkzD4ddkqVuNHtGg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1nUuU0-00GxzR-79; Thu, 17 Mar 2022 18:04:20 +0000 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1nUuTw-00GxyK-TE for linux-riscv@lists.infradead.org; Thu, 17 Mar 2022 18:04:18 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1647540255; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=EOSDI0h0ANr9PEykDMY3nNB9yGsUhPfVjoXSQ0kUYPs=; b=UebgmokPtmEiQmvESVMGEijXAjossRMfFJhr5MorrzffvEK7dmAmdbmJGwrlHj4wl0xZ8p OjqUhLi4odY+QdPKXdpPWw5rCvz7eCzmKt9MVGPjBfTLwXSdVUi0y2aG2DZQK6vIat3hW/ X0aXlwoy/VZyca8pXqPCRW0u+nK2ANo= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-78-xxlvuOx6OoCAqTVlvk_owg-1; Thu, 17 Mar 2022 14:04:11 -0400 X-MC-Unique: xxlvuOx6OoCAqTVlvk_owg-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 0064E85A5BE; Thu, 17 Mar 2022 18:04:11 +0000 (UTC) Received: from [10.22.8.95] (unknown [10.22.8.95]) by smtp.corp.redhat.com (Postfix) with ESMTP id 3DC9FC08092; Thu, 17 Mar 2022 18:04:10 +0000 (UTC) Message-ID: <7d076c5b-a17c-72c0-766f-3ae834264683@redhat.com> Date: Thu, 17 Mar 2022 14:04:09 -0400 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.5.0 Subject: Re: [PATCH 2/5] asm-generic: ticket-lock: New generic ticket-based spinlock Content-Language: en-US To: Palmer Dabbelt , linux-riscv@lists.infradead.org, peterz@infradead.org Cc: jonas@southpole.se, stefan.kristiansson@saunalahti.fi, shorne@gmail.com, mingo@redhat.com, Will Deacon , boqun.feng@gmail.com, Paul Walmsley , Palmer Dabbelt , aou@eecs.berkeley.edu, Arnd Bergmann , jszhang@kernel.org, wangkefeng.wang@huawei.com, openrisc@lists.librecores.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org References: <20220316232600.20419-1-palmer@rivosinc.com> <20220316232600.20419-3-palmer@rivosinc.com> From: Waiman Long In-Reply-To: <20220316232600.20419-3-palmer@rivosinc.com> X-Scanned-By: MIMEDefang 2.85 on 10.11.54.8 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220317_110417_066985_A24A6D2E X-CRM114-Status: GOOD ( 26.33 ) X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org On 3/16/22 19:25, Palmer Dabbelt wrote: > From: Peter Zijlstra > > This is a simple, fair spinlock. Specifically it doesn't have all the > subtle memory model dependencies that qspinlock has, which makes it more > suitable for simple systems as it is more likely to be correct. > > [Palmer: commit text] > Signed-off-by: Palmer Dabbelt > > -- > > I have specifically not included Peter's SOB on this, as he sent his > original patch > > without one. > --- > include/asm-generic/ticket-lock-types.h | 11 ++++ > include/asm-generic/ticket-lock.h | 86 +++++++++++++++++++++++++ > 2 files changed, 97 insertions(+) > create mode 100644 include/asm-generic/ticket-lock-types.h > create mode 100644 include/asm-generic/ticket-lock.h > > diff --git a/include/asm-generic/ticket-lock-types.h b/include/asm-generic/ticket-lock-types.h > new file mode 100644 > index 000000000000..829759aedda8 > --- /dev/null > +++ b/include/asm-generic/ticket-lock-types.h > @@ -0,0 +1,11 @@ > +/* SPDX-License-Identifier: GPL-2.0 */ > + > +#ifndef __ASM_GENERIC_TICKET_LOCK_TYPES_H > +#define __ASM_GENERIC_TICKET_LOCK_TYPES_H > + > +#include > +typedef atomic_t arch_spinlock_t; > + > +#define __ARCH_SPIN_LOCK_UNLOCKED ATOMIC_INIT(0) > + > +#endif /* __ASM_GENERIC_TICKET_LOCK_TYPES_H */ > diff --git a/include/asm-generic/ticket-lock.h b/include/asm-generic/ticket-lock.h > new file mode 100644 > index 000000000000..3f0d53e21a37 > --- /dev/null > +++ b/include/asm-generic/ticket-lock.h > @@ -0,0 +1,86 @@ > +/* SPDX-License-Identifier: GPL-2.0 */ > + > +/* > + * 'Generic' ticket-lock implementation. > + * > + * It relies on atomic_fetch_add() having well defined forward progress > + * guarantees under contention. If your architecture cannot provide this, stick > + * to a test-and-set lock. > + * > + * It also relies on atomic_fetch_add() being safe vs smp_store_release() on a > + * sub-word of the value. This is generally true for anything LL/SC although > + * you'd be hard pressed to find anything useful in architecture specifications > + * about this. If your architecture cannot do this you might be better off with > + * a test-and-set. > + * > + * It further assumes atomic_*_release() + atomic_*_acquire() is RCpc and hence > + * uses atomic_fetch_add() which is SC to create an RCsc lock. > + * > + * The implementation uses smp_cond_load_acquire() to spin, so if the > + * architecture has WFE like instructions to sleep instead of poll for word > + * modifications be sure to implement that (see ARM64 for example). > + * > + */ > + > +#ifndef __ASM_GENERIC_TICKET_LOCK_H > +#define __ASM_GENERIC_TICKET_LOCK_H > + > +#include > +#include > + > +static __always_inline void ticket_lock(arch_spinlock_t *lock) > +{ > + u32 val = atomic_fetch_add(1<<16, lock); /* SC, gives us RCsc */ > + u16 ticket = val >> 16; > + > + if (ticket == (u16)val) > + return; > + > + atomic_cond_read_acquire(lock, ticket == (u16)VAL); > +} > + > +static __always_inline bool ticket_trylock(arch_spinlock_t *lock) > +{ > + u32 old = atomic_read(lock); > + > + if ((old >> 16) != (old & 0xffff)) > + return false; > + > + return atomic_try_cmpxchg(lock, &old, old + (1<<16)); /* SC, for RCsc */ > +} > + > +static __always_inline void ticket_unlock(arch_spinlock_t *lock) > +{ > + u16 *ptr = (u16 *)lock + __is_defined(__BIG_ENDIAN); > + u32 val = atomic_read(lock); > + > + smp_store_release(ptr, (u16)val + 1); > +} > + > +static __always_inline int ticket_is_locked(arch_spinlock_t *lock) > +{ > + u32 val = atomic_read(lock); > + > + return ((val >> 16) != (val & 0xffff)); > +} > + > +static __always_inline int ticket_is_contended(arch_spinlock_t *lock) > +{ > + u32 val = atomic_read(lock); > + > + return (s16)((val >> 16) - (val & 0xffff)) > 1; > +} > + > +static __always_inline int ticket_value_unlocked(arch_spinlock_t lock) > +{ > + return !ticket_is_locked(&lock); > +} > + > +#define arch_spin_lock(l) ticket_lock(l) > +#define arch_spin_trylock(l) ticket_trylock(l) > +#define arch_spin_unlock(l) ticket_unlock(l) > +#define arch_spin_is_locked(l) ticket_is_locked(l) > +#define arch_spin_is_contended(l) ticket_is_contended(l) > +#define arch_spin_value_unlocked(l) ticket_value_unlocked(l) > + > +#endif /* __ASM_GENERIC_TICKET_LOCK_H */ Acked-by: Waiman Long _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv