From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lindbergh.monkeyblade.net (lindbergh.monkeyblade.net [23.128.96.19]) (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 E627417733 for ; Tue, 15 Aug 2023 22:32:18 +0000 (UTC) Received: from mail-ed1-x536.google.com (mail-ed1-x536.google.com [IPv6:2a00:1450:4864:20::536]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 00A562100 for ; Tue, 15 Aug 2023 15:32:01 -0700 (PDT) Received: by mail-ed1-x536.google.com with SMTP id 4fb4d7f45d1cf-5257f2c0773so539761a12.2 for ; Tue, 15 Aug 2023 15:32:01 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cloudflare.com; s=google; t=1692138720; x=1692743520; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:from:to:cc:subject:date :message-id:reply-to; bh=6R1K7ydUNFwtjoi/u3FY7+KS9fiu0n5Lc1EtyEIeePE=; b=eB2hYLGDWreCCGz4u7/lLVM/3mhrrmlpJmf6qykpGgYnFwjWbaWXqmpDzPRIWrbTV7 chAc0pfd09KQ7RQAMFhAP41RI2jD7JJDedvL0yl2tPrkUs6AmYdlZ6oKnnN7mEyeyztp IvP7TwBmkEMW7DgDQR4gERPEcxcrzeZ1NYUb0= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1692138720; x=1692743520; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=6R1K7ydUNFwtjoi/u3FY7+KS9fiu0n5Lc1EtyEIeePE=; b=Xedua6AtDlvUQX1WukUPl6Gw2yorJzdwEaIFGYQu0Qrs9sjn+ZNtS26E3qzLhpgyM8 sT8SnrWPvTY3bf7eZFMpnEv2r7i6fmFceRaAy3wecY5P75eF+7AzEMnznJY7TqHbLeLM fTONiyA3G5eW0tKt4I26/itctt1VkT4s/+rlqRRBa4A1bU7nDY7BCphdxaJND3rDmZv4 eH+SmL6TAenOQhwQwaqChn/eV5bndhQX7rEv/c785dOM2CALklTY6BADdm12g69KZHEv 9q/u1ucEzf3f6uDsl0D1YSEm4rhbE2i3PYwByC/SsOfW4hV7YjUtaBSQpkwAsqm31AOe P/Pw== X-Gm-Message-State: AOJu0YxYRpGc62rnonexxhYonqgw1oohWofPwT/8IqWCRv5Ua8/TMoaw zTWerpKXUSoSwyTXnkwEXG/thy2SozkAlawsdrdaMA== X-Google-Smtp-Source: AGHT+IHLnvvHpVGa2ywLMBcWm2YOrhVOII3BV6OZjuJ+ojTRMx3vBIotf2jz9W0SnMJBKanY97CG/LjI41ukHSMs1Cs= X-Received: by 2002:aa7:d1ce:0:b0:523:d1e0:7079 with SMTP id g14-20020aa7d1ce000000b00523d1e07079mr140764edp.21.1692138720456; Tue, 15 Aug 2023 15:32:00 -0700 (PDT) Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <20230814093528.117342-1-bigeasy@linutronix.de> <20230814093528.117342-3-bigeasy@linutronix.de> <25de7655-6084-e6b9-1af6-c47b3d3b7dc1@kernel.org> In-Reply-To: <25de7655-6084-e6b9-1af6-c47b3d3b7dc1@kernel.org> From: Yan Zhai Date: Tue, 15 Aug 2023 17:31:49 -0500 Message-ID: Subject: Re: [RFC PATCH 2/2] softirq: Drop the warning from do_softirq_post_smp_call_flush(). To: Jesper Dangaard Brouer Cc: Sebastian Andrzej Siewior , linux-kernel@vger.kernel.org, netdev@vger.kernel.org, "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Peter Zijlstra , Thomas Gleixner , Wander Lairson Costa , kernel-team Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF, RCVD_IN_DNSWL_BLOCKED,SPF_HELO_NONE,SPF_NONE,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net On Tue, Aug 15, 2023 at 7:08=E2=80=AFAM Jesper Dangaard Brouer wrote: > > > > On 14/08/2023 11.35, Sebastian Andrzej Siewior wrote: > > This is an undesired situation and it has been attempted to avoid the > > situation in which ksoftirqd becomes scheduled. This changed since > > commit d15121be74856 ("Revert "softirq: Let ksoftirqd do its job"") > > and now a threaded interrupt handler will handle soft interrupts at its > > end even if ksoftirqd is pending. That means that they will be processe= d > > in the context in which they were raised. > > $ git describe --contains d15121be74856 > v6.5-rc1~232^2~4 > > That revert basically removes the "overload" protection that was added > to cope with DDoS situations in Aug 2016 (Cc. Cloudflare). As described > in https://git.kernel.org/torvalds/c/4cd13c21b207 ("softirq: Let > ksoftirqd do its job") in UDP overload situations when UDP socket > receiver runs on same CPU as ksoftirqd it "falls-off-an-edge" and almost > doesn't process packets (because softirq steals CPU/sched time from UDP > pid). Warning Cloudflare (Cc) as this might affect their production > use-cases, and I recommend getting involved to evaluate the effect of > these changes. > > I do realize/acknowledge that the reverted patch caused other latency > issues, given it was a "big-hammer" approach affecting other softirq > processing (as can be seen by e.g. the watchdog fixes patches). > Thus, the revert makes sense, but how to regain the "overload" > protection such that RX networking cannot starve processes reading from > the socket? (is this what Sebastian's patchset does?) > Thanks for notifying us. We will need to evaluate if this is going to change the picture under serious floods. Yan > --Jesper > > Thread link for people Cc'ed: > https://lore.kernel.org/all/20230814093528.117342-1-bigeasy@linutronix.de= /#r