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 DC47BC46CD2 for ; Wed, 24 Jan 2024 16:13:40 +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=y3gbgjm8rj/BnMF8ri3gAWx8wi9OMj0B4VpjJD0r1BY=; b=H7I+4no4CIa8hL wpLtXxWF3INrcKKLkwZ8N+fm4Y061WsOPB0bSISPdRK/ibp8FWKoqaOYUsUZsSpmn+RAP5kufiZ9V ZPQSDkpmw3H7Kd9NJLZl1E4ST02IwN/8WQ4kkRbfXA80cZV5utlog1jZbykLzwls97D/IV8y/IU9j YOhsSRAKtb8MqJ5neA1OZwXA1Vlfsoo8N1IiFeowX9J2mIU++3fE7t6O6cn5h5Wq5f06kJKCoUtcC ug0mxnpy35onFVGNwlyW/OQ/wyG8JW8QlOWMn1b3vvTFInPQBr9g2GOHuZaO3uhk1lOTaLLCX744D 591ThjdCKGZIbsmRUnwA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1rSfsW-00487g-15; Wed, 24 Jan 2024 16:13:28 +0000 Received: from smtpout.efficios.com ([2607:5300:203:b2ee::31e5]) by bombadil.infradead.org with esmtps (Exim 4.96 #2 (Red Hat Linux)) id 1rSfsS-00485m-2X for linux-riscv@lists.infradead.org; Wed, 24 Jan 2024 16:13:26 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=efficios.com; s=smtpout1; t=1706112796; bh=CmL8wTtpgjbpskLlRLiCz6pU6cSsxxWnkQiC+ZyxVGk=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=xY69iOjQrXnkCBpDwyzUKhwkCE8wToyhDK/3oQtq3mno7+NJ9lS5u7bHrcvBOYXUp W37jFqUB1RFPHkI9qvdTseGgeOoQqsvKNCMi18/sc+3xo3Be4DAeBkCJrD/do3lp5e lkDinivWyTqeIDE+JM7Vesp97qHUE3ZQvzUtkvR5ooQk7auyVcTy2z9jKWbOU+jAP5 XCxnNL+qMU8ODg7V4xk09T3oQ1qxWTaQDWF8BKDZPQDKUP4lf0KzeC0khQ+gJEQmcg mi6Sr6NaEslo+urKskjKEnh+1w0NaA01qiopSpNdRP+Hpg+lz3rpQTaejIHiUoBlZE V6cSnQYLRYQgg== Received: from [172.16.0.134] (192-222-143-198.qc.cable.ebox.net [192.222.143.198]) by smtpout.efficios.com (Postfix) with ESMTPSA id 4TKpsS3JvnzTt5; Wed, 24 Jan 2024 11:13:16 -0500 (EST) Message-ID: Date: Wed, 24 Jan 2024 11:13:16 -0500 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 2/4] membarrier: Create Documentation/scheduler/membarrier.rst Content-Language: en-US To: Andrea Parri , paul.walmsley@sifive.com, palmer@dabbelt.com, aou@eecs.berkeley.edu, paulmck@kernel.org, corbet@lwn.net Cc: mmaas@google.com, hboehm@google.com, striker@us.ibm.com, charlie@rivosinc.com, rehn@rivosinc.com, linux-riscv@lists.infradead.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org References: <20240110145533.60234-1-parri.andrea@gmail.com> <20240110145533.60234-3-parri.andrea@gmail.com> From: Mathieu Desnoyers In-Reply-To: <20240110145533.60234-3-parri.andrea@gmail.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240124_081325_124372_5FCC9612 X-CRM114-Status: GOOD ( 23.61 ) 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 2024-01-10 09:55, Andrea Parri wrote: > To gather the architecture requirements of the "private/global > expedited" membarrier commands. The file will be expanded to > integrate further information about the membarrier syscall (as > needed/desired in the future). While at it, amend some related > inline comments in the membarrier codebase. Reviewed-by: Mathieu Desnoyers > > Suggested-by: Mathieu Desnoyers > Signed-off-by: Andrea Parri > --- > Documentation/scheduler/index.rst | 1 + > Documentation/scheduler/membarrier.rst | 37 ++++++++++++++++++++++++++ > MAINTAINERS | 1 + > kernel/sched/core.c | 7 ++++- > kernel/sched/membarrier.c | 8 +++--- > 5 files changed, 49 insertions(+), 5 deletions(-) > create mode 100644 Documentation/scheduler/membarrier.rst > > diff --git a/Documentation/scheduler/index.rst b/Documentation/scheduler/index.rst > index 3170747226f6d..43bd8a145b7a9 100644 > --- a/Documentation/scheduler/index.rst > +++ b/Documentation/scheduler/index.rst > @@ -7,6 +7,7 @@ Scheduler > > > completion > + membarrier > sched-arch > sched-bwc > sched-deadline > diff --git a/Documentation/scheduler/membarrier.rst b/Documentation/scheduler/membarrier.rst > new file mode 100644 > index 0000000000000..ab7ee3824b407 > --- /dev/null > +++ b/Documentation/scheduler/membarrier.rst > @@ -0,0 +1,37 @@ > +.. SPDX-License-Identifier: GPL-2.0 > + > +======================== > +membarrier() System Call > +======================== > + > +MEMBARRIER_CMD_{PRIVATE,GLOBAL}_EXPEDITED - Architecture requirements > +===================================================================== > + > +Memory barriers before updating rq->curr > +---------------------------------------- > + > +The command requires each architecture to have a full memory barrier after > +coming from user-space, before updating rq->curr. This barrier is implied > +by the sequence rq_lock(); smp_mb__after_spinlock() in __schedule(). The > +barrier matches a full barrier in the proximity of the membarrier system > +call exit, cf. membarrier_{private,global}_expedited(). > + > +Memory barriers after updating rq->curr > +--------------------------------------- > + > +The command requires each architecture to have a full memory barrier after > +updating rq->curr, before returning to user-space. The schemes providing > +this barrier on the various architectures are as follows. > + > + - alpha, arc, arm, hexagon, mips rely on the full barrier implied by > + spin_unlock() in finish_lock_switch(). > + > + - arm64 relies on the full barrier implied by switch_to(). > + > + - powerpc, riscv, s390, sparc, x86 rely on the full barrier implied by > + switch_mm(), if mm is not NULL; they rely on the full barrier implied > + by mmdrop(), otherwise. On powerpc and riscv, switch_mm() relies on > + membarrier_arch_switch_mm(). > + > +The barrier matches a full barrier in the proximity of the membarrier system > +call entry, cf. membarrier_{private,global}_expedited(). > diff --git a/MAINTAINERS b/MAINTAINERS > index 0f8cec504b2ba..6bce0aeecb4f2 100644 > --- a/MAINTAINERS > +++ b/MAINTAINERS > @@ -13815,6 +13815,7 @@ M: Mathieu Desnoyers > M: "Paul E. McKenney" > L: linux-kernel@vger.kernel.org > S: Supported > +F: Documentation/scheduler/membarrier.rst > F: arch/*/include/asm/membarrier.h > F: include/uapi/linux/membarrier.h > F: kernel/sched/membarrier.c > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 711dc753f7216..b51bc86f8340c 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -6599,7 +6599,9 @@ static void __sched notrace __schedule(unsigned int sched_mode) > * if (signal_pending_state()) if (p->state & @state) > * > * Also, the membarrier system call requires a full memory barrier > - * after coming from user-space, before storing to rq->curr. > + * after coming from user-space, before storing to rq->curr; this > + * barrier matches a full barrier in the proximity of the membarrier > + * system call exit. > */ > rq_lock(rq, &rf); > smp_mb__after_spinlock(); > @@ -6677,6 +6679,9 @@ static void __sched notrace __schedule(unsigned int sched_mode) > * architectures where spin_unlock is a full barrier, > * - switch_to() for arm64 (weakly-ordered, spin_unlock > * is a RELEASE barrier), > + * > + * The barrier matches a full barrier in the proximity of > + * the membarrier system call entry. > */ > ++*switch_count; > > diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c > index 2ad881d07752c..f3d91628d6b8a 100644 > --- a/kernel/sched/membarrier.c > +++ b/kernel/sched/membarrier.c > @@ -251,7 +251,7 @@ static int membarrier_global_expedited(void) > return 0; > > /* > - * Matches memory barriers around rq->curr modification in > + * Matches memory barriers after rq->curr modification in > * scheduler. > */ > smp_mb(); /* system call entry is not a mb. */ > @@ -300,7 +300,7 @@ static int membarrier_global_expedited(void) > > /* > * Memory barrier on the caller thread _after_ we finished > - * waiting for the last IPI. Matches memory barriers around > + * waiting for the last IPI. Matches memory barriers before > * rq->curr modification in scheduler. > */ > smp_mb(); /* exit from system call is not a mb */ > @@ -339,7 +339,7 @@ static int membarrier_private_expedited(int flags, int cpu_id) > return 0; > > /* > - * Matches memory barriers around rq->curr modification in > + * Matches memory barriers after rq->curr modification in > * scheduler. > */ > smp_mb(); /* system call entry is not a mb. */ > @@ -415,7 +415,7 @@ static int membarrier_private_expedited(int flags, int cpu_id) > > /* > * Memory barrier on the caller thread _after_ we finished > - * waiting for the last IPI. Matches memory barriers around > + * waiting for the last IPI. Matches memory barriers before > * rq->curr modification in scheduler. > */ > smp_mb(); /* exit from system call is not a mb */ -- Mathieu Desnoyers EfficiOS Inc. https://www.efficios.com _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv