From patchwork Wed Oct 19 22:51:38 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Paul E. McKenney" X-Patchwork-Id: 13012455 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 49A28C433FE for ; Wed, 19 Oct 2022 22:51:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230323AbiJSWvy (ORCPT ); Wed, 19 Oct 2022 18:51:54 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51210 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230287AbiJSWvu (ORCPT ); Wed, 19 Oct 2022 18:51:50 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B142218E706; Wed, 19 Oct 2022 15:51:48 -0700 (PDT) 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 dfw.source.kernel.org (Postfix) with ESMTPS id 03065619DA; Wed, 19 Oct 2022 22:51:48 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1870AC43147; Wed, 19 Oct 2022 22:51:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1666219907; bh=wIrUnsZvsb76w0mrU4ByciwxrnTRBZTUwIx2ZrTZP6w=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=DplQmogbLIlmDKw7nrrkuSAqXJXVs56ONOkM2rhX3C0kvLWKXYoh/417+tAnrpZEH /XuVKaH1KLnf6KdOFX2VmVHU1OPwbqZJCUsalOicFa/EQfbFMh8v5UCoAdMzeCxLB/ IusxzzT3D5rqNr95x3L8lhNofkrHcbYbX19fPfMGLU6vnB6hspmzVYOQLX+0TvgiIv OihWC3yew5drgwauQAe4qmjLQ7JdAXWeAfPm2HOu21tWurXsguQLGSqEm53bOZvrlR 8GTuYwQmOpX2OfLBnKqcqwJHtCXXMYGDFHTPXKQVq1kMk25UIle0wLQ/PrWeIhE/5e z62Ggq6tADgvg== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 844165C0B8F; Wed, 19 Oct 2022 15:51:46 -0700 (PDT) From: "Paul E. McKenney" To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com, rostedt@goodmis.org, "Joel Fernandes (Google)" , "Paul E . McKenney" Subject: [PATCH rcu 08/14] percpu-refcount: Use call_rcu_flush() for atomic switch Date: Wed, 19 Oct 2022 15:51:38 -0700 Message-Id: <20221019225144.2500095-8-paulmck@kernel.org> X-Mailer: git-send-email 2.31.1.189.g2e36527f23 In-Reply-To: <20221019225138.GA2499943@paulmck-ThinkPad-P17-Gen-1> References: <20221019225138.GA2499943@paulmck-ThinkPad-P17-Gen-1> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org From: "Joel Fernandes (Google)" call_rcu() changes to save power will slow down the percpu refcounter's "per-CPU to atomic switch" path. The primitive uses RCU when switching to atomic mode. The enqueued async callback wakes up waiters waiting in the percpu_ref_switch_waitq. Due to this, per-CPU refcount users will slow down, such as blk_pre_runtime_suspend(). Use the call_rcu_flush() API instead which reverts to the old behavior. Signed-off-by: Joel Fernandes (Google) Signed-off-by: Paul E. McKenney --- lib/percpu-refcount.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/lib/percpu-refcount.c b/lib/percpu-refcount.c index e5c5315da2741..65c58a029297d 100644 --- a/lib/percpu-refcount.c +++ b/lib/percpu-refcount.c @@ -230,7 +230,8 @@ static void __percpu_ref_switch_to_atomic(struct percpu_ref *ref, percpu_ref_noop_confirm_switch; percpu_ref_get(ref); /* put after confirmation */ - call_rcu(&ref->data->rcu, percpu_ref_switch_to_atomic_rcu); + call_rcu_flush(&ref->data->rcu, + percpu_ref_switch_to_atomic_rcu); } static void __percpu_ref_switch_to_percpu(struct percpu_ref *ref)