From nobody Tue Oct 7 14:51:39 2025 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8050528EC1C; Wed, 9 Jul 2025 10:46:15 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752057975; cv=none; b=NOjobmSRsPv8HYsRUAENfqAMbiulnevPH2qE3tLcDBMLI/gKGS+xDKhSj3rFS2nVnssDmu2dMWznFY6+r7SNydPEFhijegdDcoFdxGa556z27FPuzEXo5seRRru2kYhQ8c3QirofmYVHwg9xkrp1ByzunVOeHHr1azJujy53AYs= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752057975; c=relaxed/simple; bh=8GTuELIWEWxwQDkgCyoSIjG7otZYJYRfYglBdDVAc0s=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=Wc26GGOrCQKYdEaZyTnGX3+FzGkpm7iDU+qDoYc25gn/sHvsvA+OcfiiNSPR0hfInYLn5ZeGjKf7YgbOqi5PCn1/pG+LVQCwnXszey8dUVW7aQVY/USrm11YVc/rRxSRHVBT7IJOWGIYPHZBwI51iDHqnckQ3AYUzvVcjpda5Ck= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Vh0ekbKd; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Vh0ekbKd" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 34813C4CEEF; Wed, 9 Jul 2025 10:46:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1752057975; bh=8GTuELIWEWxwQDkgCyoSIjG7otZYJYRfYglBdDVAc0s=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Vh0ekbKdJVLwKq1Fmmie+dhsX26iQZXbXGzyvJ0HWpdtqbkYJUDApYBSpPKvMA1d1 pJwLoNQpVCnUUMUwkPrJ408H+W2tNlUDu0pq0qRx9/MMKEHBQg2BrX98YMyEIpTaOm SuxGpaBMnSghwiY2XIB/Xaxry/l3h8grCknzLjVIIY7hPnr5F6Gr7gvJCC7ifMe6Du BXtC62u4O8EvQBISQPMMQO4vS/vKLS/chVIwM/GyPq+mDEQjLb8oyyK26EWn1x9cLo P9PzogaWHBHCDJceqBctX8LT6hY+NSEVp/vOeX06ZeAn5JobcGsrjtg3RRsL29uToo ZtL4iKrvm+v9w== From: neeraj.upadhyay@kernel.org To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, paulmck@kernel.org, joelagnelf@nvidia.com, frederic@kernel.org, boqun.feng@gmail.com, urezki@gmail.com, rostedt@goodmis.org, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com, qiang.zhang1211@gmail.com, neeraj.iitr10@gmail.com, neeraj.upadhyay@amd.com, "Neeraj Upadhyay (AMD)" , Andrii Nakryiko , Alexei Starovoitov Subject: [PATCH rcu 1/3] srcu: Expedite SRCU-fast grace periods Date: Wed, 9 Jul 2025 16:15:53 +0530 Message-Id: <20250709104555.15670-2-neeraj.upadhyay@kernel.org> X-Mailer: git-send-email 2.40.1 In-Reply-To: <20250709104555.15670-1-neeraj.upadhyay@kernel.org> References: <20250709104555.15670-1-neeraj.upadhyay@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: "Paul E. McKenney" Currently, SRCU-fast grace periods use synchronize_rcu() to provide the needed ordering with readers, even given an expedited SRCU-fast grace period, which isn't all that expedited. This commit therefore instead uses synchronize_rcu_expedited() if there is an expedited SRCU-fast grace period in flight. Of course, given an non-expedited SRCU-fast grace period blocked in synchronize_rcu(), a later request for an expedited SRCU-fast grace period will wait for that synchronize_rcu() to return before switching to use of synchronize_rcu_expedited(). If this turns out to be a real problem for a production workload, we can increase the complexity (but likely also degrade the energy efficiency) to speed things up further. Signed-off-by: Paul E. McKenney Cc: Andrii Nakryiko Cc: Alexei Starovoitov Signed-off-by: Neeraj Upadhyay (AMD) --- kernel/rcu/srcutree.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index 48047260697e..c5e8ebc493d5 100644 --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -502,6 +502,8 @@ static bool srcu_readers_active_idx_check(struct srcu_s= truct *ssp, int idx) */ if (!did_gp) smp_mb(); /* A */ + else if (srcu_gp_is_expedited(ssp)) + synchronize_rcu_expedited(); /* X */ else synchronize_rcu(); /* X */ =20 --=20 2.40.1