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=-9.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 14093C4363A for ; Wed, 21 Oct 2020 06:06:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8BC2B22249 for ; Wed, 21 Oct 2020 06:06:12 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=mg.codeaurora.org header.i=@mg.codeaurora.org header.b="dzEmI08j" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2440699AbgJUGFl (ORCPT ); Wed, 21 Oct 2020 02:05:41 -0400 Received: from m42-4.mailgun.net ([69.72.42.4]:63070 "EHLO m42-4.mailgun.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2440690AbgJUGFk (ORCPT ); Wed, 21 Oct 2020 02:05:40 -0400 DKIM-Signature: a=rsa-sha256; v=1; c=relaxed/relaxed; d=mg.codeaurora.org; q=dns/txt; s=smtp; t=1603260339; h=Message-ID: References: In-Reply-To: Subject: Cc: To: From: Date: Content-Transfer-Encoding: Content-Type: MIME-Version: Sender; bh=SMFQdg25ll68aWs3gXbCBgwGSJf2TTUzhzCc7hHd9cU=; b=dzEmI08j6hDxStTw68WtDphV5Ka2FARCdDhFKJbo0/l5KTzy4GBynezfzj723QIqNhqyce6g FYtS16QvX4rSHEaexRAS/IklvPWv6EXufxmatZkBOf7UmY5b3182tlQ+jqzq2+5rF7VqrgjY mL9BX0CWgC8YdcEcL39jGInS4Ik= X-Mailgun-Sending-Ip: 69.72.42.4 X-Mailgun-Sid: WyI0MWYwYSIsICJsaW51eC1rZXJuZWxAdmdlci5rZXJuZWwub3JnIiwgImJlOWU0YSJd 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-east-1.postgun.com with SMTP id 5f8fcfa9588858a304cf77db (version=TLS1.2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256); Wed, 21 Oct 2020 06:05:29 GMT Sender: cang=codeaurora.org@mg.codeaurora.org Received: by smtp.codeaurora.org (Postfix, from userid 1001) id E9531C433FE; Wed, 21 Oct 2020 06:05:28 +0000 (UTC) Received: from mail.codeaurora.org (localhost.localdomain [127.0.0.1]) (using TLSv1 with cipher ECDHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) (Authenticated sender: cang) by smtp.codeaurora.org (Postfix) with ESMTPSA id BA0A1C433CB; Wed, 21 Oct 2020 06:05:27 +0000 (UTC) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Wed, 21 Oct 2020 14:05:27 +0800 From: Can Guo To: jaegeuk@kernel.org Cc: linux-kernel@vger.kernel.org, linux-scsi@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, kernel-team@android.com, Alim Akhtar , Avri Altman Subject: Re: [PATCH v2 5/5] scsi: ufs: fix clkgating on/off correctly In-Reply-To: <20201021045213.GB3004521@google.com> References: <20201020195258.2005605-1-jaegeuk@kernel.org> <20201020195258.2005605-6-jaegeuk@kernel.org> <2a8ecc4185b3a5411077f4e3fc66000f@codeaurora.org> <20201021045213.GB3004521@google.com> Message-ID: X-Sender: cang@codeaurora.org User-Agent: Roundcube Webmail/1.3.9 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020-10-21 12:52, jaegeuk@kernel.org wrote: > On 10/21, Can Guo wrote: >> On 2020-10-21 03:52, Jaegeuk Kim wrote: >> > The below call stack prevents clk_gating at every IO completion. >> > We can remove the condition, ufshcd_any_tag_in_use(), since >> > clkgating_work >> > will check it again. >> > >> >> I think checking ufshcd_any_tag_in_use() in either ufshcd_release() or >> gate_work() can break UFS clk gating's functionality. >> >> ufshcd_any_tag_in_use() was introduced to replace hba->lrb_in_use. >> However, >> they are not exactly same - ufshcd_any_tag_in_use() returns true if >> any tag >> assigned from block layer is still in use, but tags are released >> asynchronously >> (through block softirq), meaning it does not reflect the real >> occupation of >> UFS host. >> That is after UFS host finishes all tasks, ufshcd_any_tag_in_use() can >> still >> return true. >> >> This change only removes the check of ufshcd_any_tag_in_use() in >> ufshcd_release(), >> but having the check of it in gate_work() can still prevent gating >> from >> happening. >> The current change works for you maybe because the tags are release >> before >> hba->clk_gating.delay_ms expires, but if hba->clk_gating.delay_ms is >> shorter >> or >> somehow block softirq is retarded, gate_work() may have chance to see >> ufshcd_any_tag_in_use() >> returns true. What do you think? > > I don't think this breaks clkgating, but fix the wrong condition check > which > prevented gate_work at all. As you mentioned, even if this schedules > gate_work > by racy conditions, gate_work will handle it as a last resort. > If clocks cannot be gated after the last task is cleared from UFS host, then clk gating is broken, no? Assume UFS has completed the last task in its queue, as this change says, ufshcd_any_tag_in_use() is preventing ufshcd_release() from invoking gate_work(). Similarly, ufshcd_any_tag_in_use() can prevent gate_work() from doing its real work - disabling the clocks. Do you agree? if (hba->clk_gating.active_reqs || hba->ufshcd_state != UFSHCD_STATE_OPERATIONAL || ufshcd_any_tag_in_use(hba) || hba->outstanding_tasks || hba->active_uic_cmd || hba->uic_async_done) goto rel_lock; Thanks, Can Guo. >> >> Thanks, >> >> Can Guo. >> >> In __ufshcd_transfer_req_compl >> Ihba->lrb_in_use is cleared immediately when UFS driver >> finishes all tasks >> >> > ufshcd_complete_requests(struct ufs_hba *hba) >> > ufshcd_transfer_req_compl() >> > __ufshcd_transfer_req_compl() >> > __ufshcd_release(hba) >> > if (ufshcd_any_tag_in_use() == 1) >> > return; >> > ufshcd_tmc_handler(hba); >> > blk_mq_tagset_busy_iter(); >> > >> > Cc: Alim Akhtar >> > Cc: Avri Altman >> > Cc: Can Guo >> > Signed-off-by: Jaegeuk Kim >> > --- >> > drivers/scsi/ufs/ufshcd.c | 2 +- >> > 1 file changed, 1 insertion(+), 1 deletion(-) >> > >> > diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c >> > index b5ca0effe636..cecbd4ace8b4 100644 >> > --- a/drivers/scsi/ufs/ufshcd.c >> > +++ b/drivers/scsi/ufs/ufshcd.c >> > @@ -1746,7 +1746,7 @@ static void __ufshcd_release(struct ufs_hba *hba) >> > >> > if (hba->clk_gating.active_reqs || hba->clk_gating.is_suspended || >> > hba->ufshcd_state != UFSHCD_STATE_OPERATIONAL || >> > - ufshcd_any_tag_in_use(hba) || hba->outstanding_tasks || >> > + hba->outstanding_tasks || >> > hba->active_uic_cmd || hba->uic_async_done) >> > return;