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=-12.4 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham 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 2EA47C433E0 for ; Thu, 30 Jul 2020 17:21:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0733D20829 for ; Thu, 30 Jul 2020 17:21:13 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=dd-wrt.com header.i=@dd-wrt.com header.b="FIoDxjeu" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728543AbgG3RVL (ORCPT ); Thu, 30 Jul 2020 13:21:11 -0400 Received: from mail.as201155.net ([185.84.6.188]:31288 "EHLO mail.as201155.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726353AbgG3RVL (ORCPT ); Thu, 30 Jul 2020 13:21:11 -0400 Received: from smtps.newmedia-net.de ([2a05:a1c0:0:de::167]:54510 helo=webmail.newmedia-net.de) by mail.as201155.net with esmtps (TLSv1:DHE-RSA-AES256-SHA:256) (Exim 4.82_1-5b7a7c0-XX) (envelope-from ) id 1k1CEs-0005yp-2X; Thu, 30 Jul 2020 19:21:06 +0200 X-CTCH-RefID: str=0001.0A782F17.5F230182.005D,ss=1,re=0.000,recu=0.000,reip=0.000,cl=1,cld=1,fgs=0 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=dd-wrt.com; s=mikd; h=Content-Transfer-Encoding:Content-Type:In-Reply-To:MIME-Version:Date:Message-ID:From:References:Cc:To:Subject; bh=g26FjbxVUABEUOyEi0P4Kxobh0qYUIuASKlvLhVTGlo=; b=FIoDxjeu4HhFNmRkS6YSO9Lr/3SjEut4Uv24zVYJ7fy3GI/PxgYEpPa5BAKyF95pMl4ml0OOsxHNUsFauca7Uj5ai50eGiv7gWMuCkDEr78H2boaanrbpyj3jT4O7XFgCfdUXvQ9DvjfU3HzydIXWofK36w2zbFl77E9kJWRRHk=; Subject: Re: [PATCH] net: add support for threaded NAPI polling To: Eric Dumazet , Felix Fietkau , netdev@vger.kernel.org Cc: Hillf Danton References: <20200729165058.83984-1-nbd@nbd.name> <866c7d83-868d-120e-f535-926c4cc9e615@gmail.com> <5aa0c26f-d3f1-b33f-a598-e4727d6f10f0@dd-wrt.com> <5eb18175-b5b9-6e4e-2541-7533e21ccb21@gmail.com> From: Sebastian Gottschall Message-ID: Date: Thu, 30 Jul 2020 19:21:05 +0200 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:79.0) Gecko/20100101 Thunderbird/79.0 MIME-Version: 1.0 In-Reply-To: <5eb18175-b5b9-6e4e-2541-7533e21ccb21@gmail.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit X-Received: from [2a01:7700:8040:300:315c:d267:8dd:d539] by webmail.newmedia-net.de with esmtpsa (TLSv1:AES128-SHA:128) (Exim 4.72) (envelope-from ) id 1k1CEs-00062t-GF; Thu, 30 Jul 2020 19:21:06 +0200 Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Am 30.07.2020 um 18:08 schrieb Eric Dumazet: > > On 7/30/20 7:30 AM, Sebastian Gottschall wrote: >> Am 29.07.2020 um 19:44 schrieb Eric Dumazet: >>> On 7/29/20 9:50 AM, Felix Fietkau wrote: >>>> For some drivers (especially 802.11 drivers), doing a lot of work in the NAPI >>>> poll function does not perform well. Since NAPI poll is bound to the CPU it >>>> was scheduled from, we can easily end up with a few very busy CPUs spending >>>> most of their time in softirq/ksoftirqd and some idle ones. >>>> >>>> Introduce threaded NAPI for such drivers based on a workqueue. The API is the >>>> same except for using netif_threaded_napi_add instead of netif_napi_add. >>>> >>>> In my tests with mt76 on MT7621 using threaded NAPI + a thread for tx scheduling >>>> improves LAN->WLAN bridging throughput by 10-50%. Throughput without threaded >>>> NAPI is wildly inconsistent, depending on the CPU that runs the tx scheduling >>>> thread. >>>> >>>> With threaded NAPI, throughput seems stable and consistent (and higher than >>>> the best results I got without it). >>>> >>>> Based on a patch by Hillf Danton >>>> >>>> Cc: Hillf Danton >>>> Signed-off-by: Felix Fietkau >>>> --- >>>> Changes since RFC v2: >>>> - fix unused but set variable reported by kbuild test robot >>>> >>>> Changes since RFC: >>>> - disable softirq around threaded poll functions >>>> - reuse most parts of napi_poll() >>>> - fix re-schedule condition >>>> >>>>   include/linux/netdevice.h |  23 ++++++ >>>>   net/core/dev.c            | 162 ++++++++++++++++++++++++++------------ >>>>   2 files changed, 133 insertions(+), 52 deletions(-) >>>> >>>> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h >>>> index ac2cd3f49aba..3a39211c7598 100644 >>>> --- a/include/linux/netdevice.h >>>> +++ b/include/linux/netdevice.h >>>> @@ -347,6 +347,7 @@ struct napi_struct { >>>>       struct list_head    dev_list; >>>>       struct hlist_node    napi_hash_node; >>>>       unsigned int        napi_id; >>>> +    struct work_struct    work; >>>>   }; >>>>     enum { >>>> @@ -357,6 +358,7 @@ enum { >>>>       NAPI_STATE_HASHED,    /* In NAPI hash (busy polling possible) */ >>>>       NAPI_STATE_NO_BUSY_POLL,/* Do not add in napi_hash, no busy polling */ >>>>       NAPI_STATE_IN_BUSY_POLL,/* sk_busy_loop() owns this NAPI */ >>>> +    NAPI_STATE_THREADED,    /* Use threaded NAPI */ >>>>   }; >>>>     enum { >>>> @@ -367,6 +369,7 @@ enum { >>>>       NAPIF_STATE_HASHED     = BIT(NAPI_STATE_HASHED), >>>>       NAPIF_STATE_NO_BUSY_POLL = BIT(NAPI_STATE_NO_BUSY_POLL), >>>>       NAPIF_STATE_IN_BUSY_POLL = BIT(NAPI_STATE_IN_BUSY_POLL), >>>> +    NAPIF_STATE_THREADED     = BIT(NAPI_STATE_THREADED), >>>>   }; >>>>     enum gro_result { >>>> @@ -2315,6 +2318,26 @@ static inline void *netdev_priv(const struct net_device *dev) >>>>   void netif_napi_add(struct net_device *dev, struct napi_struct *napi, >>>>               int (*poll)(struct napi_struct *, int), int weight); >>>>   +/** >>>> + *    netif_threaded_napi_add - initialize a NAPI context >>>> + *    @dev:  network device >>>> + *    @napi: NAPI context >>>> + *    @poll: polling function >>>> + *    @weight: default weight >>>> + * >>>> + * This variant of netif_napi_add() should be used from drivers using NAPI >>>> + * with CPU intensive poll functions. >>>> + * This will schedule polling from a high priority workqueue that >>>> + */ >>>> +static inline void netif_threaded_napi_add(struct net_device *dev, >>>> +                       struct napi_struct *napi, >>>> +                       int (*poll)(struct napi_struct *, int), >>>> +                       int weight) >>>> +{ >>>> +    set_bit(NAPI_STATE_THREADED, &napi->state); >>>> +    netif_napi_add(dev, napi, poll, weight); >>>> +} >>>> + >>>>   /** >>>>    *    netif_tx_napi_add - initialize a NAPI context >>>>    *    @dev:  network device >>>> diff --git a/net/core/dev.c b/net/core/dev.c >>>> index 19f1abc26fcd..11b027f3a2b9 100644 >>>> --- a/net/core/dev.c >>>> +++ b/net/core/dev.c >>>> @@ -158,6 +158,7 @@ static DEFINE_SPINLOCK(offload_lock); >>>>   struct list_head ptype_base[PTYPE_HASH_SIZE] __read_mostly; >>>>   struct list_head ptype_all __read_mostly;    /* Taps */ >>>>   static struct list_head offload_base __read_mostly; >>>> +static struct workqueue_struct *napi_workq __read_mostly; >>>>     static int netif_rx_internal(struct sk_buff *skb); >>>>   static int call_netdevice_notifiers_info(unsigned long val, >>>> @@ -6286,6 +6287,11 @@ void __napi_schedule(struct napi_struct *n) >>>>   { >>>>       unsigned long flags; >>>>   +    if (test_bit(NAPI_STATE_THREADED, &n->state)) { >>>> +        queue_work(napi_workq, &n->work); >>>> +        return; >>>> +    } >>>> + >>> Where is the corresponding cancel_work_sync() or flush_work() at device dismantle ? >>> >>> Just hoping the thread will eventually run seems optimistic to me. >>> >>> >>> Quite frankly, I do believe this STATE_THREADED status should be a generic NAPI attribute >>> that can be changed dynamically, at admin request, instead of having to change/recompile >>> a driver. >> thats not that easy. wifi devices do use dummy netdev devices. they are not visible to sysfs and other administrative options. >> so changing it would just be possible if a special mac80211 based control would be implemented for these drivers. >> for standard netdev devices it isnt a big thing to implement a administrative control by sysfs (if you are talking about such a feature) > We do not want to add code in fast path only for one device. We need something truly generic. > > I am not saying only the admin can chose, it is fine if a driver does not give the choice > and will simply call netif_threaded_napi_add() what could make sense if the feature can be disabled / enabled, but it will only affect drivers using the netif_threaded_napi_add call, but it should not affect drivers using the old api in any way since not all drivers will work with this feature.