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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no 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 2F7D5C43461 for ; Fri, 14 May 2021 21:54:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0C8E160C40 for ; Fri, 14 May 2021 21:54:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233435AbhENVzM (ORCPT ); Fri, 14 May 2021 17:55:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39216 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230097AbhENVzL (ORCPT ); Fri, 14 May 2021 17:55:11 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A4D63C06174A; Fri, 14 May 2021 14:53:59 -0700 (PDT) From: Thomas Gleixner DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1621029236; 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: in-reply-to:in-reply-to:references:references; bh=YMDSuhwDDAIBz65ztaPmnouscCan/8FmST0Xl3cL+3o=; b=jiN3KFXCr2sxwoVmItCe+621oLau+r8o6ATT5UrfWPjZ+BCjeAEdMydDsG0LjGUfI+4Lcu YFc+yGssUeWlmFa6SY/kb3dlHS7iomFIJgcI6FOjE7QHExHZkMJlcaa7Gc3a/difbbXETY ppXPgWWzulrWg/Vk6p1qHypxbAd1nJi8xFhegAhyS5rF8pPltslF/iuyIpQIJtHtSMPftI gDl30hZOM5QvfLjGfULqdpgcJKHbdnLuXlWGTy3QUE0LKP8wuDocHx5gWLENiYgTDSEmO/ rXDefewkUJOxOoXFhitTJAKeoztmWM9yNzBfFWfmmeVhHm92oKdquyT7B8Na+w== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1621029236; 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: in-reply-to:in-reply-to:references:references; bh=YMDSuhwDDAIBz65ztaPmnouscCan/8FmST0Xl3cL+3o=; b=PxoAkGINkifPynLBMaZAZB3REJRuHaHqAa7rAIPjXpll7B7jY7w5IBWEsZ9tWgE2qlt0rz 6Za0D/MJPDbe49CQ== To: Alison Chaiken , Jakub Kicinski Cc: Sebastian Andrzej Siewior , netdev@vger.kernel.org, Juri Lelli , linux-rt-users , Steven Rostedt , LKML , sassmann@redhat.com, "David S. Miller" , stable-rt@vger.kernel.org Subject: Re: [PATCH net-next] net: Treat __napi_schedule_irqoff() as __napi_schedule() on PREEMPT_RT In-Reply-To: References: <20210512214324.hiaiw3e2tzmsygcz@linutronix.de> <87k0o360zx.ffs@nanos.tec.linutronix.de> <20210514115649.6c84fdc3@kicinski-fedora-PC1C0HJN> Date: Fri, 14 May 2021 23:53:56 +0200 Message-ID: <877dk12d8r.ffs@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, May 14 2021 at 12:44, Alison Chaiken wrote: > On Fri, May 14, 2021 at 11:56 AM Jakub Kicinski wrote: >> >> Another thing while I have your attention - ____napi_schedule() does >> __raise_softirq_irqoff() which AFAIU does not wake the ksoftirq thread. >> On non-RT we get occasional NOHZ warnings when drivers schedule napi >> from process context, but on RT this is even more of a problem, right? >> ksoftirqd won't run until something else actually wakes it up? > > By "NOHZ warnings," do you mean "NOHZ: local_softirq_pending"? We see > that message about once a week with 4.19. Presumably any failure of > ____napi_schedule() to wake ksoftirqd could only cause problems for the > NET_RX softirq, so if the pending softirq is different, the cause lies > elsewhere. If you read the above carefully you might notice that this _IS_ about ____napi_schedule() being invoked from task context which raises NET_RX and then results in pending 08! which is NET_RX. Thanks, tglx