From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753200AbdKNEF0 (ORCPT ); Mon, 13 Nov 2017 23:05:26 -0500 Received: from mail-oi0-f65.google.com ([209.85.218.65]:51892 "EHLO mail-oi0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751171AbdKNEFX (ORCPT ); Mon, 13 Nov 2017 23:05:23 -0500 X-Google-Smtp-Source: AGs4zMap0MZsbwViWlLsm4kzygRw4as7W5KSNszCYZm+fG3OwJEo5qKOmSV5NRbALJGYp5V5vp9TPA== Subject: Re: [PATCH RFC v3 4/6] Documentation: Add three sysctls for smart idle poll To: Ingo Molnar , Quan Xu Cc: kvm@vger.kernel.org, linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, x86@kernel.org, Yang Zhang References: <1510570064-6178-1-git-send-email-quan.xu0@gmail.com> <20171113150842.epdffyxhlu5nq37u@gmail.com> From: Quan Xu Message-ID: <35da8c93-95fb-8bf0-8538-4e1ef5f126f4@gmail.com> Date: Tue, 14 Nov 2017 12:05:16 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0 MIME-Version: 1.0 In-Reply-To: <20171113150842.epdffyxhlu5nq37u@gmail.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2017/11/13 23:08, Ingo Molnar wrote: > * Quan Xu wrote: > >> From: Quan Xu >> >> To reduce the cost of poll, we introduce three sysctl to control the >> poll time when running as a virtual machine with paravirt. >> >> Signed-off-by: Yang Zhang >> Signed-off-by: Quan Xu >> --- >> Documentation/sysctl/kernel.txt | 35 +++++++++++++++++++++++++++++++++++ >> arch/x86/kernel/paravirt.c | 4 ++++ >> include/linux/kernel.h | 6 ++++++ >> kernel/sysctl.c | 34 ++++++++++++++++++++++++++++++++++ >> 4 files changed, 79 insertions(+), 0 deletions(-) >> >> diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt >> index 694968c..30c25fb 100644 >> --- a/Documentation/sysctl/kernel.txt >> +++ b/Documentation/sysctl/kernel.txt >> @@ -714,6 +714,41 @@ kernel tries to allocate a number starting from this one. >> >> ============================================================== >> >> +paravirt_poll_grow: (X86 only) >> + >> +Multiplied value to increase the poll time. This is expected to take >> +effect only when running as a virtual machine with CONFIG_PARAVIRT >> +enabled. This can't bring any benifit on bare mental even with >> +CONFIG_PARAVIRT enabled. >> + >> +By default this value is 2. Possible values to set are in range {2..16}. >> + >> +============================================================== >> + >> +paravirt_poll_shrink: (X86 only) >> + >> +Divided value to reduce the poll time. This is expected to take effect >> +only when running as a virtual machine with CONFIG_PARAVIRT enabled. >> +This can't bring any benifit on bare mental even with CONFIG_PARAVIRT >> +enabled. >> + >> +By default this value is 2. Possible values to set are in range {2..16}. >> + >> +============================================================== >> + >> +paravirt_poll_threshold_ns: (X86 only) >> + >> +Controls the maximum poll time before entering real idle path. This is >> +expected to take effect only when running as a virtual machine with >> +CONFIG_PARAVIRT enabled. This can't bring any benifit on bare mental >> +even with CONFIG_PARAVIRT enabled. >> + >> +By default, this value is 0 means not to poll. Possible values to set >> +are in range {0..500000}. Change the value to non-zero if running >> +latency-bound workloads in a virtual machine. > I absolutely hate it how this hybrid idle loop polling mechanism is not > self-tuning! Ingo, actually it is self-tuning.. > Please make it all work fine by default, and automatically so, instead of adding > three random parameters... .. I will make it all fine by default. howerver cloud environment is of diversity, could I only leave paravirt_poll_threshold_ns parameter (the maximum poll time), which is as similar as "adaptive halt-polling" Wanpeng mentioned.. then user can turn it off, or find an appropriate threshold for some odd scenario.. thanks for your comments!! Quan Alibaba Cloud > And if it cannot be done automatically then we should rather not do it at all. > Maybe the next submitter of a similar feature can think of a better approach. > > Thanks, > > Ingo >