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 X-Spam-Level: X-Spam-Status: No, score=-15.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A2329C64E69 for ; Tue, 24 Nov 2020 05:19:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3C6AD206FB for ; Tue, 24 Nov 2020 05:19:11 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=mg.codeaurora.org header.i=@mg.codeaurora.org header.b="F4MXGhIL" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727660AbgKXFTK (ORCPT ); Tue, 24 Nov 2020 00:19:10 -0500 Received: from z5.mailgun.us ([104.130.96.5]:44477 "EHLO z5.mailgun.us" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725616AbgKXFTJ (ORCPT ); Tue, 24 Nov 2020 00:19:09 -0500 DKIM-Signature: a=rsa-sha256; v=1; c=relaxed/relaxed; d=mg.codeaurora.org; q=dns/txt; s=smtp; t=1606195148; h=Content-Transfer-Encoding: Content-Type: In-Reply-To: MIME-Version: Date: Message-ID: From: References: Cc: To: Subject: Sender; bh=OSRlY2cqO6ILnbjsSHLPCyv/v8iXY7wncAy0NJ3RYX0=; b=F4MXGhILfQrsxwlcPdv9JnAv5IZSHwfN9YyF4KMumM+DypfBATmAnNZ6HY4SnfzYIlW9X/fa iYPzDuQzcf19Wv0/SGuFA56+FTA69NIRYKzxvF4EkhFTO45hSu/Zp/wtx6DAVAb1s+dBMUDF mf+BM6hMqUpPmoPd7oLPo7xSdCA= X-Mailgun-Sending-Ip: 104.130.96.5 X-Mailgun-Sid: WyI0MWYwYSIsICJsaW51eC1rZXJuZWxAdmdlci5rZXJuZWwub3JnIiwgImJlOWU0YSJd Received: from smtp.codeaurora.org (ec2-35-166-182-171.us-west-2.compute.amazonaws.com [35.166.182.171]) by smtp-out-n04.prod.us-west-2.postgun.com with SMTP id 5fbc97ca7e9d874dfc3cb0e0 (version=TLS1.2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256); Tue, 24 Nov 2020 05:19:06 GMT Sender: neeraju=codeaurora.org@mg.codeaurora.org Received: by smtp.codeaurora.org (Postfix, from userid 1001) id 92508C43467; Tue, 24 Nov 2020 05:19:06 +0000 (UTC) Received: from [192.168.0.101] (unknown [49.206.49.183]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) (Authenticated sender: neeraju) by smtp.codeaurora.org (Postfix) with ESMTPSA id F055DC433ED; Tue, 24 Nov 2020 05:18:59 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org F055DC433ED Authentication-Results: aws-us-west-2-caf-mail-1.web.codeaurora.org; dmarc=none (p=none dis=none) header.from=codeaurora.org Authentication-Results: aws-us-west-2-caf-mail-1.web.codeaurora.org; spf=fail smtp.mailfrom=neeraju@codeaurora.org Subject: Re: [PATCH v2 tip/core/rcu 1/6] srcu: Make Tiny SRCU use multi-bit grace-period counter To: paulmck@kernel.org Cc: rcu@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com, mingo@kernel.org, jiangshanlai@gmail.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org, kent.overstreet@gmail.com References: <@@@> <20201121005919.17152-1-paulmck@kernel.org> <20201123195543.GC1437@paulmck-ThinkPad-P72> From: Neeraj Upadhyay Message-ID: <46f5137b-2450-2478-6274-157367264ce4@codeaurora.org> Date: Tue, 24 Nov 2020 10:48:57 +0530 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.5.0 MIME-Version: 1.0 In-Reply-To: <20201123195543.GC1437@paulmck-ThinkPad-P72> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/24/2020 1:25 AM, Paul E. McKenney wrote: > On Mon, Nov 23, 2020 at 10:01:13AM +0530, Neeraj Upadhyay wrote: >> On 11/21/2020 6:29 AM, paulmck@kernel.org wrote: >>> From: "Paul E. McKenney" >>> >>> There is a need for a polling interface for SRCU grace periods. This >>> polling needs to distinguish between an SRCU instance being idle on the >>> one hand or in the middle of a grace period on the other. This commit >>> therefore converts the Tiny SRCU srcu_struct structure's srcu_idx from >>> a defacto boolean to a free-running counter, using the bottom bit to >>> indicate that a grace period is in progress. The second-from-bottom >>> bit is thus used as the index returned by srcu_read_lock(). >>> >>> Link: https://lore.kernel.org/rcu/20201112201547.GF3365678@moria.home.lan/ >>> Reported-by: Kent Overstreet >>> [ paulmck: Fix __srcu_read_lock() idx computation Neeraj per Upadhyay. ] >>> Signed-off-by: Paul E. McKenney >>> --- >>> include/linux/srcutiny.h | 4 ++-- >>> kernel/rcu/srcutiny.c | 5 +++-- >>> 2 files changed, 5 insertions(+), 4 deletions(-) >>> >>> diff --git a/include/linux/srcutiny.h b/include/linux/srcutiny.h >>> index 5a5a194..d9edb67 100644 >>> --- a/include/linux/srcutiny.h >>> +++ b/include/linux/srcutiny.h >>> @@ -15,7 +15,7 @@ >>> struct srcu_struct { >>> short srcu_lock_nesting[2]; /* srcu_read_lock() nesting depth. */ >>> - short srcu_idx; /* Current reader array element. */ >>> + unsigned short srcu_idx; /* Current reader array element in bit 0x2. */ >>> u8 srcu_gp_running; /* GP workqueue running? */ >>> u8 srcu_gp_waiting; /* GP waiting for readers? */ >>> struct swait_queue_head srcu_wq; >>> @@ -59,7 +59,7 @@ static inline int __srcu_read_lock(struct srcu_struct *ssp) >>> { >>> int idx; >>> - idx = READ_ONCE(ssp->srcu_idx); >>> + idx = ((READ_ONCE(ssp->srcu_idx) + 1) & 0x2) >> 1; >>> WRITE_ONCE(ssp->srcu_lock_nesting[idx], ssp->srcu_lock_nesting[idx] + 1); >>> return idx; >>> } >> >> Need change in idx calcultion in srcu_torture_stats_print() ? >> >> static inline void srcu_torture_stats_print(struct srcu_struct *ssp, >> idx = READ_ONCE(ssp->srcu_idx) & 0x1; > > Excellent point! It should match the calculation in __srcu_read_lock(), > shouldn't it? I have updated this, thank you! > > Thanx, Paul > Updated version looks good! Thanks Neeraj >> Thanks >> Neeraj >> >>> diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c >>> index 6208c1d..5598cf6 100644 >>> --- a/kernel/rcu/srcutiny.c >>> +++ b/kernel/rcu/srcutiny.c >>> @@ -124,11 +124,12 @@ void srcu_drive_gp(struct work_struct *wp) >>> ssp->srcu_cb_head = NULL; >>> ssp->srcu_cb_tail = &ssp->srcu_cb_head; >>> local_irq_enable(); >>> - idx = ssp->srcu_idx; >>> - WRITE_ONCE(ssp->srcu_idx, !ssp->srcu_idx); >>> + idx = (ssp->srcu_idx & 0x2) / 2; >>> + WRITE_ONCE(ssp->srcu_idx, ssp->srcu_idx + 1); >>> WRITE_ONCE(ssp->srcu_gp_waiting, true); /* srcu_read_unlock() wakes! */ >>> swait_event_exclusive(ssp->srcu_wq, !READ_ONCE(ssp->srcu_lock_nesting[idx])); >>> WRITE_ONCE(ssp->srcu_gp_waiting, false); /* srcu_read_unlock() cheap. */ >>> + WRITE_ONCE(ssp->srcu_idx, ssp->srcu_idx + 1); >>> /* Invoke the callbacks we removed above. */ >>> while (lh) { >>> >> >> -- >> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of >> the Code Aurora Forum, hosted by The Linux Foundation -- QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, hosted by The Linux Foundation