From patchwork Tue Jan 17 12:29:07 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jesper Dangaard Brouer X-Patchwork-Id: 13104589 X-Patchwork-Delegate: kuba@kernel.org 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 03287C3DA78 for ; Tue, 17 Jan 2023 12:30:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236272AbjAQMaA (ORCPT ); Tue, 17 Jan 2023 07:30:00 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53354 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235993AbjAQM36 (ORCPT ); Tue, 17 Jan 2023 07:29:58 -0500 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E738A35275 for ; Tue, 17 Jan 2023 04:29:14 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1673958554; 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; bh=crjrU81uLtw8WwH5QvegQxiaaSw28nWKODPrHB2mY3M=; b=DqJDuPmP7alP36dVb6uCaHqRG76avBf9utMQBlN4qIC2+tnb7xWhNr3kRQd60+FZTpw4r0 l3G9PwCscf9/QUSf8cTcD+ZNfJtzOH+8MnhXyjoCRAP7U1Sr56v2nxr03hP02idbJ8+ltx A/ibtgq80WkVnD1z7XkNfOf+Hpm8eb4= 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-523-dZA_k3azMQmuar0YZreNbw-1; Tue, 17 Jan 2023 07:29:09 -0500 X-MC-Unique: dZA_k3azMQmuar0YZreNbw-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 9B1F218E0045; Tue, 17 Jan 2023 12:29:08 +0000 (UTC) Received: from firesoul.localdomain (ovpn-208-34.brq.redhat.com [10.40.208.34]) by smtp.corp.redhat.com (Postfix) with ESMTP id 5C4D84085720; Tue, 17 Jan 2023 12:29:08 +0000 (UTC) Received: from [192.168.42.3] (localhost [IPv6:::1]) by firesoul.localdomain (Postfix) with ESMTP id 4B48730721A6C; Tue, 17 Jan 2023 13:29:07 +0100 (CET) Subject: [PATCH net-next] net: avoid irqsave in skb_defer_free_flush From: Jesper Dangaard Brouer To: netdev@vger.kernel.org Cc: Jesper Dangaard Brouer , Jakub Kicinski , "David S. Miller" , edumazet@google.com, pabeni@redhat.com Date: Tue, 17 Jan 2023 13:29:07 +0100 Message-ID: <167395854720.539380.12918805302179692095.stgit@firesoul> User-Agent: StGit/1.4 MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.2 Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org X-Patchwork-Delegate: kuba@kernel.org The spin_lock irqsave/restore API variant in skb_defer_free_flush can be replaced with the faster spin_lock irq variant, which doesn't need to read and restore the CPU flags. Using the unconditional irq "disable/enable" API variant is safe, because the skb_defer_free_flush() function is only called during NAPI-RX processing in net_rx_action(), where it is known the IRQs are enabled. Expected gain is 14 cycles from avoiding reading and restoring CPU flags in a spin_lock_irqsave/restore operation, measured via a microbencmark kernel module[1] on CPU E5-1650 v4 @ 3.60GHz. Microbenchmark overhead of spin_lock+unlock: - spin_lock_unlock_irq cost: 34 cycles(tsc) 9.486 ns - spin_lock_unlock_irqsave cost: 48 cycles(tsc) 13.567 ns We don't expect to see a measurable packet performance gain, as skb_defer_free_flush() is called infrequently once per NIC device NAPI bulk cycle and conditionally only if SKBs have been deferred by other CPUs via skb_attempt_defer_free(). [1] https://github.com/netoptimizer/prototype-kernel/blob/master/kernel/lib/time_bench_sample.c Signed-off-by: Jesper Dangaard Brouer Reviewed-by: Jacob Keller Reviewed-by: Jacob Keller --- net/core/dev.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/net/core/dev.c b/net/core/dev.c index cf78f35bc0b9..9c60190fe352 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -6616,17 +6616,16 @@ static int napi_threaded_poll(void *data) static void skb_defer_free_flush(struct softnet_data *sd) { struct sk_buff *skb, *next; - unsigned long flags; /* Paired with WRITE_ONCE() in skb_attempt_defer_free() */ if (!READ_ONCE(sd->defer_list)) return; - spin_lock_irqsave(&sd->defer_lock, flags); + spin_lock_irq(&sd->defer_lock); skb = sd->defer_list; sd->defer_list = NULL; sd->defer_count = 0; - spin_unlock_irqrestore(&sd->defer_lock, flags); + spin_unlock_irq(&sd->defer_lock); while (skb != NULL) { next = skb->next;