Received: by 2002:ac0:bc90:0:0:0:0:0 with SMTP id a16csp3275948img; Mon, 25 Mar 2019 07:13:01 -0700 (PDT) X-Google-Smtp-Source: APXvYqzIPIIbEImPi+xKAsjUPfAVI9lHGcIiA6afW/1LNeygtbN36x9C8/m2pdXAM0r/kwCNa1Le X-Received: by 2002:a63:6786:: with SMTP id b128mr14166531pgc.318.1553523181618; Mon, 25 Mar 2019 07:13:01 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1553523181; cv=none; d=google.com; s=arc-20160816; b=ist+UmHJiauUz67SUwAKVjyHRMyqmi+kCp5FhEe8/XgMR1t9wMQZ0VeSVa4/1o36lL 5WnF8DhJoW9reQZBQdFVdA9fSQXVK2WuOshNfBuFWlGmkaUhdn1brpo7FqLi0WzptJ8v Uapp3q7BwihxX99zTiuC4y4zGDOAwuDFijhvfXZ9DcsXDxucQ5iC8IVGimi8uTQusfia hUhzl2cTw8Gse9PSmKvuar16EiqPWVyJrMEkx4o/8fJW7VwtIWRrVH+eOJGXsKXkHPUs wgsOyXiiKcMoBNpASLGFdG4S41obODQm4T9y9CvdT+BqmZxF05rVNPj2apvRzHTC8yK4 cz9A== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:sender:user-agent:in-reply-to :content-disposition:mime-version:references:message-id:subject:cc :to:from:date:dkim-signature; bh=KTt93h75wJmE7jV6jCleD3fv2thkBfT2D18E2mIVZzA=; b=ha8qgp5mvbNoyrRrrT22KmS6oyB7ANbUaBjThUesQ4fhexB0/AH7+A7QF89sgg5ZW9 RPR96//3U90Pr//GLtwe7meggrbQMyDeCDWnWirJopP4hPAWgTdbqwyqqfpSNu6idWGw QYj1GU6pEfv8ErnjpvcPbKQ8VhA4GFk0F/nYAql0PXuC4l3tYM0DdbdSYiHboMtU8PAV HRX5ECleS6IqNK8ZUGNpg/sd7soDVGtUptJYOgXwb29uHlW/3fUWt/HeXOUBqpW6ufVe nz/CA83P2a8oOvlEuongYsnBgwOrzLc97OnHzlTas5+g++eCwZCBUK8iG2fXyG5F241a +zYg== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=lQqJdZHJ; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com Return-Path: Received: from vger.kernel.org (vger.kernel.org. [209.132.180.67]) by mx.google.com with ESMTP id f4si13180524pgv.118.2019.03.25.07.12.45; Mon, 25 Mar 2019 07:13:01 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=lQqJdZHJ; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726128AbfCYOL6 (ORCPT + 99 others); Mon, 25 Mar 2019 10:11:58 -0400 Received: from mail-yw1-f66.google.com ([209.85.161.66]:46928 "EHLO mail-yw1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725355AbfCYOL5 (ORCPT ); Mon, 25 Mar 2019 10:11:57 -0400 Received: by mail-yw1-f66.google.com with SMTP id v127so7102532ywe.13 for ; Mon, 25 Mar 2019 07:11:57 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=KTt93h75wJmE7jV6jCleD3fv2thkBfT2D18E2mIVZzA=; b=lQqJdZHJ6UcPCjywy2RwjHTQh0ANBIl+04G15xC+jF06ooEmgZg4AJYpJ3UgX9nlhb UWrv2nOqqhCcoWXRs+3jxpOfuGdbIEiXCETU2ZwXzVM6Ybn4AT/spneX6zcCeNqAy+VY ClDPIrjs4m8Z61P3TzyIXEmYUyR+4UuuNobyBjU5AiZX+Fgd5mP4Z8fAvvhMhNRAyNak atOPMmu/uH17V9Tn6R+NQgnlGzO1exy9RbnulNsl/xtVi80dh9K57BZXJUMcpcLinSI5 QcHyd0zlEo0ocHb0UIFCNEIoYRGzslm+o6REHXetwyp2Ivx6m9V6ttvpUAJy4RsAkaha 353A== 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=KTt93h75wJmE7jV6jCleD3fv2thkBfT2D18E2mIVZzA=; b=i1Jj6+b2CgPD1M8Tna9aZW0fcz78wVuCPD6wkG5HVilxSrovwz8WzOhA4yKQ3RYdM2 Hp34fd/P2bt2M2EBEeht8fS5/Q6K1jSWaZwa4p9qMHUVvcy2LdPgW6fkpL7TjO0KQSOg +pAIgRDS4K/KK8n5evN56eOiYijIw3Bllp27O95eWDTiaasSmhSb4JMluUpXE7naZKbd H236HcIoMQYCeQjuOwenJ9aSqyvRWMSyBhne49695IMB7fWMQ+lS23ft3n4IpNhczlfu mO7gKPjGK2x1vkuSdDlXfC+P3w1Mmn8U2duwLykvV+T6zypX2v2Zpy5Uv/14t0bB3QNz gxYg== X-Gm-Message-State: APjAAAWgUn9frAdBxKAhdMtc1+GRzvJeevmH2+twRCZv216mNooqwj6R L+iroInVCsUFuzk0RV30xeI= X-Received: by 2002:a25:d20d:: with SMTP id j13mr21035429ybg.417.1553523117103; Mon, 25 Mar 2019 07:11:57 -0700 (PDT) Received: from centos-dev.localdomain (pool-173-66-89-81.washdc.fios.verizon.net. [173.66.89.81]) by smtp.gmail.com with ESMTPSA id i189sm5631147ywa.73.2019.03.25.07.11.55 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 25 Mar 2019 07:11:56 -0700 (PDT) Date: Mon, 25 Mar 2019 10:11:38 -0400 From: Ryan Thibodeaux To: Boris Ostrovsky Cc: luca abeni , Dario Faggioli , xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org, oleksandr_andrushchenko@epam.com, tglx@linutronix.de, jgross@suse.com, ryan.thibodeaux@starlab.io Subject: Re: [PATCH] x86/xen: Add "xen_timer_slop" command line option Message-ID: <20190325141138.GA44413@centos-dev.localdomain> References: <1553279397-130201-1-git-send-email-ryan.thibodeaux@starlab.io> <52bfeae7c256faec444b69efe58d363ad60c3fc5.camel@suse.com> <20190323114151.5cebf31b@sweethome> <20190325130530.56603806@luca64> <69e40698-f7ae-11c3-e4b7-dda4f1fadcf6@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <69e40698-f7ae-11c3-e4b7-dda4f1fadcf6@oracle.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Mar 25, 2019 at 09:43:20AM -0400, Boris Ostrovsky wrote: > On 3/25/19 8:05 AM, luca abeni wrote: > > Hi all, > > > > On Sat, 23 Mar 2019 11:41:51 +0100 > > luca abeni wrote: > > [...] > >>>> Is there any data that shows effects of using this new parameter? > >>>> > >>> Yes, I've done some research and experiments on this. I did it > >>> together with a friend, which I'm Cc-ing, as I'm not sure we're > >>> ready/capable to share the results, yet (Luca?). > >> I think we can easily share the experimental data (cyclictest output > >> and plots). > >> > >> Moreover, we can share the scripts and tools for running the > >> experiments (so, everyone can easily reproduce the numbers by simply > >> typing "make" and waiting for some time :) > >> > >> > >> I'll try to package the results and the scripts/tools this evening, > >> and I'll send them. > > Sorry for the delay. I put some quick results here: > > http://retis.santannapisa.it/luca/XenTimers/ > > (there also is a link to the scripts to be used for reproducing the > > results). The latencies have been measured by running cyclictest in the > > guest (see the scripts for details). > > > > The picture shows the latencies measured with an unpatched guest kernel > > and with a guest kernel having TIMER_SLOP set to 1000 (arbitrary small > > value :). > > All the experiments have been performed booting the hypervisor with a > > small timer_slop (the hypervisor's one) value. So, they show that > > decreasing the hypervisor's timer_slop is not enough to measure low > > latencies with cyclictest. > > > > I have a couple of questions: > * Does it make sense to make this a tunable for other clockevent devices > as well? I gather that would be on a case-by-case basis for very specific ones. For many timers in the kernel, the minimums are determined by the actual hardware backing the timer, and the minimum can be adjusted by the clockevent code. This case is special since it is entirely a software-based implementation in the kernel, where the actual timer implementation is in the Xen hypervisor. > * This patch adjusts min value. Could max value (ever) need a similar > adjustment? I cannot think of such a case where that would be helpful, but I cannot rule that out or speak as an authority. - Ryan