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=-2.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 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 EA408C433DF for ; Fri, 12 Jun 2020 05:29:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C80C5207F7 for ; Fri, 12 Jun 2020 05:29:10 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linaro.org header.i=@linaro.org header.b="dk3ugeAE" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726396AbgFLF3B (ORCPT ); Fri, 12 Jun 2020 01:29:01 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57298 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726300AbgFLF3B (ORCPT ); Fri, 12 Jun 2020 01:29:01 -0400 Received: from mail-pg1-x52a.google.com (mail-pg1-x52a.google.com [IPv6:2607:f8b0:4864:20::52a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CAD84C08C5C1 for ; Thu, 11 Jun 2020 22:28:59 -0700 (PDT) Received: by mail-pg1-x52a.google.com with SMTP id e9so3602635pgo.9 for ; Thu, 11 Jun 2020 22:28:59 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=sn8Q2QTIJp4z3aJYpXX1ZHPFtT0KGOrsa14hJOj2CZ4=; b=dk3ugeAESJZcB7Ib32BwlQGgfx9iTvtwl1PuBEikxgRo0Lc4TtKRi/8Xi2tYQC/z6Q KM/rkoZDO2B3Vv+BV/qKKsEdHASexOfVLUWpEpXby0ddy7vegM42ltm/7YlidZkGXL0j T72ZH63bHrOfLmKNiPoWWBfGFumnggDr1CGNgMOw92+0KZvZTNSskiMm82+LjGyUoY5R 2/5dD1b/x0KUfQAS8eAkSu8+/oXb59fy+4zMwQlmbYNTcjQVB9ubXOT0ReEB+k8zt21C D/uS7AKn5xQhG7c6hZ7A8gAN1oMOwXNexQuDSoEovnBE0nrC/yM44wL5x2lLAdlrUFfN mjvg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=sn8Q2QTIJp4z3aJYpXX1ZHPFtT0KGOrsa14hJOj2CZ4=; b=Q5U8NvxN+caZ7+fGJIglWa9G+QAERRkWB1i40moTegkgprQRnsc7hYfS8wdDrArKVN +qiK+hXPA9pZ+BlFq2ZxH++dhHO/O2mTxic1zLgstAZRunAywcUK2M8bua3rtmHH7rq3 RLzsiO4DfNLNHtu44yOl4srA8Rgc7dcGi0uspgkmPOXjRLndgdaXHG6LKJxGWAGvnMrW +fbp6Y93okwQlUAuD8gkLCSKw7RZiCk9llPNtiztT81ZlEXiyHWHHqBJ3tvT0Sdyjkbn DO6v3532FEtY5NLczJY4L7ocrU1tpOoGwefplffwKe4s3pqgvVXfuYmWaJGeGoWlxdV2 h6eA== X-Gm-Message-State: AOAM530xyoUrblZUHegBdEiCdbeWYvf8NlQy/AiNyfj/wqOGqIYVCkBW SXr+n8mIcfjdMWN2/axO53UGUg== X-Google-Smtp-Source: ABdhPJyHqEKil6Mou/zBNdyhF9uHnkjkpxj+ljkhROJsCnXD4KjAtn8p08f6zo/SXq+4izoXTulfCw== X-Received: by 2002:a62:e40f:: with SMTP id r15mr10236310pfh.247.1591939738558; Thu, 11 Jun 2020 22:28:58 -0700 (PDT) Received: from localhost ([122.172.62.209]) by smtp.gmail.com with ESMTPSA id u14sm5369429pfk.211.2020.06.11.22.28.57 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Thu, 11 Jun 2020 22:28:57 -0700 (PDT) Date: Fri, 12 Jun 2020 10:58:53 +0530 From: Viresh Kumar To: Jassi Brar Cc: Sudeep Holla , Rob Herring , Arnd Bergmann , Frank Rowand , Bjorn Andersson , Vincent Guittot , linux-arm-kernel , Devicetree List , Linux Kernel Mailing List Subject: Re: [RFC] dt-bindings: mailbox: add doorbell support to ARM MHU Message-ID: <20200612052853.nds4iycie6ldjnnr@vireshk-i7> References: <20200604092052.GD8814@bogus> <20200605045645.GD12397@bogus> <20200605085830.GA32372@bogus> <20200610093334.yznxl2esv5ht27ns@vireshk-i7> <20200611100027.GB18781@bogus> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20180716-391-311a52 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11-06-20, 19:34, Jassi Brar wrote: > In the first post in this thread, Viresh lamented that mailbox > introduces "a few ms" delay in the scheduler path. > Your own tests show that is certainly not the case -- average is the > same as proposed virtual channels 50-100us, the best case is 3us vs > 53us for virtual channels. Hmmm, I am not sure where is the confusion here Jassi. There are two things which are very very different from each other. - Time taken by the mailbox framework (and remote for acknowledging it) for completion of a single request, this can be 3us to 100s of us. This is clear for everyone. THIS IS NOT THE PROBLEM. - Delay introduced by few of such requests on the last one, i.e. 5 normal requests followed by an important one (like DVFS), the last one needs to wait for the first 5 to finish first. THIS IS THE PROBLEM. Just increasing the timeout isn't going to solve anything as I said in the last email, we can make it 5 minutes for what's its worth. The idea is to make the turn-around-time less for all the requests.. >From Google (I know you must already know it, I am just trying to highlight the importance of this thing here): Turnaround time (TAT) is the time interval from the time of submission of a process (read request) to the time of the completion of the process. This is what people care about, that is the whole reason kernel has multi-processing support in the first place. If making things sequential was good enough, we would have never reached here. The whole idea is to parallelize things as much as possible without hurting efficiency in a bad way (like too much parallelism). The hardware allows parallelism and there is absolutely no point in not allowing that. The kernel doesn't need to worry about how the remote is going to handle it. Remote may be simple and handle it sequentially or it may be running Linux itself and can schedule multiple threads for requests. -- viresh