From patchwork Sun Jul 12 22:36:05 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Kiyanovski, Arthur" X-Patchwork-Id: 1327619 X-Patchwork-Delegate: davem@davemloft.net Return-Path: X-Original-To: patchwork-incoming-netdev@ozlabs.org Delivered-To: patchwork-incoming-netdev@ozlabs.org Authentication-Results: ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=vger.kernel.org (client-ip=23.128.96.18; helo=vger.kernel.org; envelope-from=netdev-owner@vger.kernel.org; receiver=) Authentication-Results: ozlabs.org; dmarc=pass (p=quarantine dis=none) header.from=amazon.com Authentication-Results: ozlabs.org; dkim=pass (1024-bit key; unprotected) header.d=amazon.com header.i=@amazon.com header.a=rsa-sha256 header.s=amazon201209 header.b=Jnty4RQZ; dkim-atps=neutral Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by ozlabs.org (Postfix) with ESMTP id 4B4hTS6yPZz9sR4 for ; Mon, 13 Jul 2020 08:36:28 +1000 (AEST) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727932AbgGLWg2 (ORCPT ); Sun, 12 Jul 2020 18:36:28 -0400 Received: from smtp-fw-6002.amazon.com ([52.95.49.90]:32500 "EHLO smtp-fw-6002.amazon.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727785AbgGLWg1 (ORCPT ); Sun, 12 Jul 2020 18:36:27 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.com; i=@amazon.com; q=dns/txt; s=amazon201209; t=1594593386; x=1626129386; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version; bh=N7nICK7RQ4ZF6EkZCqxyyd5Tqn4vCMEg08dZm5sMI6g=; b=Jnty4RQZaxPUE/jbavv4jr6X9cUG83mK07vpoWPnSvs0QP94ARu82a9V q67s/GGOLNtNITw96U4pI6UH/capxltM3CMx7xeSYmnRdtl3jowVGVH41 BHCF22PMei76LYF+ATFC/1WTxG+tZPiiQAdM43plpvKEVID2mqNzwC56y 0=; IronPort-SDR: 5LuhC4WQQwUfnRFay4LSfFhSBRPOuf/h9G8W9I+qL3+h8MxwdX4ku2Ixn4IWbqnmvkn/NSpPSg pUO+zANspMww== X-IronPort-AV: E=Sophos;i="5.75,345,1589241600"; d="scan'208";a="41374726" Received: from iad12-co-svc-p1-lb1-vlan3.amazon.com (HELO email-inbound-relay-2b-4ff6265a.us-west-2.amazon.com) ([10.43.8.6]) by smtp-border-fw-out-6002.iad6.amazon.com with ESMTP; 12 Jul 2020 22:36:25 +0000 Received: from EX13MTAUWA001.ant.amazon.com (pdx4-ws-svc-p6-lb7-vlan3.pdx.amazon.com [10.170.41.166]) by email-inbound-relay-2b-4ff6265a.us-west-2.amazon.com (Postfix) with ESMTPS id 8C3F4A0688; Sun, 12 Jul 2020 22:36:24 +0000 (UTC) Received: from EX13D10UWA003.ant.amazon.com (10.43.160.248) by EX13MTAUWA001.ant.amazon.com (10.43.160.58) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Sun, 12 Jul 2020 22:36:23 +0000 Received: from EX13MTAUWA001.ant.amazon.com (10.43.160.58) by EX13D10UWA003.ant.amazon.com (10.43.160.248) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Sun, 12 Jul 2020 22:36:22 +0000 Received: from HFA15-G63729NC.amazon.com (10.1.212.5) by mail-relay.amazon.com (10.43.160.118) with Microsoft SMTP Server id 15.0.1497.2 via Frontend Transport; Sun, 12 Jul 2020 22:36:18 +0000 From: To: , CC: Arthur Kiyanovski , , , , , , , , , , , , , , Subject: [PATCH V2 net-next 1/7] net: ena: avoid unnecessary rearming of interrupt vector when busy-polling Date: Mon, 13 Jul 2020 01:36:05 +0300 Message-ID: <1594593371-14045-2-git-send-email-akiyano@amazon.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1594593371-14045-1-git-send-email-akiyano@amazon.com> References: <1594593371-14045-1-git-send-email-akiyano@amazon.com> MIME-Version: 1.0 Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org From: Arthur Kiyanovski In napi busy-poll mode, the kernel invokes the napi handler of the device repeatedly to poll the NIC's receive queues. This process repeats until a timeout, specific for each connection, is up. By polling packets in busy-poll mode the user may gain lower latency and higher throughput (since the kernel no longer waits for interrupts to poll the queues) in expense of CPU usage. Upon completing a napi routine, the driver checks whether the routine was called by an interrupt handler. If so, the driver re-enables interrupts for the device. This is needed since an interrupt routine invocation disables future invocations until explicitly re-enabled. The driver avoids re-enabling the interrupts if they were not disabled in the first place (e.g. if driver in busy mode). Originally, the driver checked whether interrupt re-enabling is needed by reading the 'ena_napi->unmask_interrupt' variable. This atomic variable was set upon interrupt and cleared after re-enabling it. In the 4.10 Linux version, the 'napi_complete_done' call was changed so that it returns 'false' when device should not re-enable interrupts, and 'true' otherwise. The change includes reading the "NAPIF_STATE_IN_BUSY_POLL" flag to check if the napi call is in busy-poll mode, and if so, return 'false'. The driver was changed to re-enable interrupts according to this routine's return value. The Linux community rejected the use of the 'ena_napi->unmaunmask_interrupt' variable to determine whether unmasking is needed, and urged to use napi_napi_complete_done() return value solely. See https://lore.kernel.org/patchwork/patch/741149/ for more details As explained, a busy-poll session exists for a specified timeout value, after which it exits the busy-poll mode and re-enters it later. This leads to many invocations of the napi handler where napi_complete_done() false indicates that interrupts should be re-enabled. This creates a bug in which the interrupts are re-enabled unnecessarily. To reproduce this bug: 1) echo 50 | sudo tee /proc/sys/net/core/busy_poll 2) echo 50 | sudo tee /proc/sys/net/core/busy_read 3) Add counters that check whether 'ena_unmask_interrupt(tx_ring, rx_ring);' is called without disabling the interrupts in the first place (i.e. with calling the interrupt routine ena_intr_msix_io()) Steps 1+2 enable busy-poll as the default mode for new connections. The busy poll routine rearms the interrupts after every session by design, and so we need to add an extra check that the interrupts were masked in the first place. Signed-off-by: Shay Agroskin Signed-off-by: Arthur Kiyanovski --- drivers/net/ethernet/amazon/ena/ena_netdev.c | 7 ++++++- drivers/net/ethernet/amazon/ena/ena_netdev.h | 1 + 2 files changed, 7 insertions(+), 1 deletion(-) diff --git a/drivers/net/ethernet/amazon/ena/ena_netdev.c b/drivers/net/ethernet/amazon/ena/ena_netdev.c index 91be3ffa1c5c..90c0fe15cd23 100644 --- a/drivers/net/ethernet/amazon/ena/ena_netdev.c +++ b/drivers/net/ethernet/amazon/ena/ena_netdev.c @@ -1913,7 +1913,9 @@ static int ena_io_poll(struct napi_struct *napi, int budget) /* Update numa and unmask the interrupt only when schedule * from the interrupt context (vs from sk_busy_loop) */ - if (napi_complete_done(napi, rx_work_done)) { + if (napi_complete_done(napi, rx_work_done) && + READ_ONCE(ena_napi->interrupts_masked)) { + WRITE_ONCE(ena_napi->interrupts_masked, false); /* We apply adaptive moderation on Rx path only. * Tx uses static interrupt moderation. */ @@ -1961,6 +1963,9 @@ static irqreturn_t ena_intr_msix_io(int irq, void *data) ena_napi->first_interrupt = true; + WRITE_ONCE(ena_napi->interrupts_masked, true); + smp_wmb(); /* write interrupts_masked before calling napi */ + napi_schedule_irqoff(&ena_napi->napi); return IRQ_HANDLED; diff --git a/drivers/net/ethernet/amazon/ena/ena_netdev.h b/drivers/net/ethernet/amazon/ena/ena_netdev.h index ba030d260940..89304b403995 100644 --- a/drivers/net/ethernet/amazon/ena/ena_netdev.h +++ b/drivers/net/ethernet/amazon/ena/ena_netdev.h @@ -167,6 +167,7 @@ struct ena_napi { struct ena_ring *rx_ring; struct ena_ring *xdp_ring; bool first_interrupt; + bool interrupts_masked; u32 qid; struct dim dim; };