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=-6.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, 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 F1F89C00A89 for ; Mon, 2 Nov 2020 18:17:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AB5A220786 for ; Mon, 2 Nov 2020 18:17:34 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=mg.codeaurora.org header.i=@mg.codeaurora.org header.b="cwc9e4vE" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726355AbgKBSRc (ORCPT ); Mon, 2 Nov 2020 13:17:32 -0500 Received: from z5.mailgun.us ([104.130.96.5]:39180 "EHLO z5.mailgun.us" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726351AbgKBSRb (ORCPT ); Mon, 2 Nov 2020 13:17:31 -0500 DKIM-Signature: a=rsa-sha256; v=1; c=relaxed/relaxed; d=mg.codeaurora.org; q=dns/txt; s=smtp; t=1604341051; h=Date: Message-Id: Cc: To: References: In-Reply-To: From: Subject: Content-Transfer-Encoding: MIME-Version: Content-Type: Sender; bh=WNliksh7Tgt2rSG29nRcv/foFEK09F28vFf8eMxlTdA=; b=cwc9e4vE9XU32H6yh64BrE350Ifd1acgO2sG0b0B/L/w1m2QahxUAeftSh4qgw5eyUEYSkTv 28NmlaYF1O5zrj2CGNIlhHTdiPE+pM6w3Y3E64+1qGLFEOcHpFtTDt94tP3rH5Vt6bpa74m+ dRjbxANzw2ZVD/9vTCLpQV8WC8M= X-Mailgun-Sending-Ip: 104.130.96.5 X-Mailgun-Sid: WyI3YTAwOSIsICJsaW51eC13aXJlbGVzc0B2Z2VyLmtlcm5lbC5vcmciLCAiYmU5ZTRhIl0= Received: from smtp.codeaurora.org (ec2-35-166-182-171.us-west-2.compute.amazonaws.com [35.166.182.171]) by smtp-out-n07.prod.us-west-2.postgun.com with SMTP id 5fa04d3a23306fb6029782d8 (version=TLS1.2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256); Mon, 02 Nov 2020 18:17:30 GMT Sender: kvalo=codeaurora.org@mg.codeaurora.org Received: by smtp.codeaurora.org (Postfix, from userid 1001) id D9788C433C9; Mon, 2 Nov 2020 18:17:30 +0000 (UTC) Received: from potku.adurom.net (88-114-240-156.elisa-laajakaista.fi [88.114.240.156]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) (Authenticated sender: kvalo) by smtp.codeaurora.org (Postfix) with ESMTPSA id 9052AC433F0; Mon, 2 Nov 2020 18:17:29 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org 9052AC433F0 Authentication-Results: aws-us-west-2-caf-mail-1.web.codeaurora.org; dmarc=none (p=none dis=none) header.from=codeaurora.org Authentication-Results: aws-us-west-2-caf-mail-1.web.codeaurora.org; spf=fail smtp.mailfrom=kvalo@codeaurora.org Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Subject: Re: [PATCH] iwlwifi: pcie: limit memory read spin time From: Kalle Valo In-Reply-To: References: To: Luca Coelho Cc: linux-wireless@vger.kernel.org User-Agent: pwcli/0.1.0-git (https://github.com/kvalo/pwcli/) Python/3.5.2 Message-Id: <20201102181730.D9788C433C9@smtp.codeaurora.org> Date: Mon, 2 Nov 2020 18:17:30 +0000 (UTC) Precedence: bulk List-ID: X-Mailing-List: linux-wireless@vger.kernel.org Luca Coelho wrote: > From: Johannes Berg > > When we read device memory, we lock a spinlock, write the address we > want to read from the device and then spin in a loop reading the data > in 32-bit quantities from another register. > > As the description makes clear, this is rather inefficient, incurring > a PCIe bus transaction for every read. In a typical device today, we > want to read 786k SMEM if it crashes, leading to 192k register reads. > Occasionally, we've seen the whole loop take over 20 seconds and then > triggering the soft lockup detector. > > Clearly, it is unreasonable to spin here for such extended periods of > time. > > To fix this, break the loop down into an outer and an inner loop, and > break out of the inner loop if more than half a second elapsed. To > avoid too much overhead, check for that only every 128 reads, though > there's no particular reason for that number. Then, unlock and relock > to obtain NIC access again, reprogram the start address and continue. > > This will keep (interrupt) latencies on the CPU down to a reasonable > time. > > Signed-off-by: Johannes Berg > Signed-off-by: Mordechay Goodstein > Signed-off-by: Luca Coelho Patch applied to wireless-drivers.git, thanks. 04516706bb99 iwlwifi: pcie: limit memory read spin time -- https://patchwork.kernel.org/project/linux-wireless/patch/iwlwifi.20201022165103.45878a7e49aa.I3b9b9c5a10002915072312ce75b68ed5b3dc6e14@changeid/ https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches