From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtpout.efficios.com (smtpout.efficios.com [167.114.26.122]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6456C176226; Fri, 12 Jul 2024 17:28:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=167.114.26.122 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1720805320; cv=none; b=DO49leCgrpfecVbV6i0PPAXOSeoS5Z3OWcy77ZNusHSyU3QPVPF2u/Ee4vfX+OVIgv4PVAyov6Gp+Z0EBSN61MadJiXS1YpeRxbzDkok+nEeSkD3QrxAHiJD43Dn4CL2elG37wfKTDJlwe4f3C8Te+nzskoCIeW/Rg6zRRV69pE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1720805320; c=relaxed/simple; bh=UcTTM2UQHQ4zFDkXWD/5VaZUWSmGXcw8UKCyFji3gw4=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=huX6ZZjWdjS1I2w16jv3Cbakyj9ki37VHakyfXY70NWZwrodo5OX/ACnL9Oitbi7IeiGDQuQZpsmVcplJhBEq7XQadjb1w7HCRwpolvlixhZpb6kcdKcmMKnf709dBmP5E6dTZCgD68sGn8lA6TpfTjAQIrtWHGHYLi05Hgc/OU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=efficios.com; spf=pass smtp.mailfrom=efficios.com; dkim=pass (2048-bit key) header.d=efficios.com header.i=@efficios.com header.b=VVdKgrqv; arc=none smtp.client-ip=167.114.26.122 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=efficios.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=efficios.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=efficios.com header.i=@efficios.com header.b="VVdKgrqv" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=efficios.com; s=smtpout1; t=1720805317; bh=UcTTM2UQHQ4zFDkXWD/5VaZUWSmGXcw8UKCyFji3gw4=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=VVdKgrqv2/7mtNAtMHYbV+pTsERp820wzE8AzVmkI2K4N2/FO4PiX+LiH3G3FpWue kwJoHLOAuTkklI7hgXT4meBpczcWMj56EfNx80Eqn70ZiWNGv5FNTVyYtRmmVm9R4j WQG+UnpJpuf0tLj2/4xs4QUvWictu9/2uWHIlOLGl22M8Wh32eRyLnw0XWXFd2MeJH dog55HB+cvS5hr5H8US9N3bKVYPeXWuIYOsMkSg4GhYAiyNK435qWZ1r0qlbvLjzws iscLT8G3Fzuf7DrTZimonW7InojSSjaz7u2LZFV7FVQp9xwMwFuMYVNQsFIK3/S8xU gUuc61XpjiGUA== Received: from [172.16.0.134] (192-222-143-198.qc.cable.ebox.net [192.222.143.198]) by smtpout.efficios.com (Postfix) with ESMTPSA id 4WLJTw4Jnfz19Px; Fri, 12 Jul 2024 13:28:36 -0400 (EDT) Message-ID: Date: Fri, 12 Jul 2024 13:28:36 -0400 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v2 0/5] Paravirt Scheduling (Dynamic vcpu priority management) To: Joel Fernandes Cc: Vineeth Remanan Pillai , Sean Christopherson , Ben Segall , Borislav Petkov , Daniel Bristot de Oliveira , Dave Hansen , Dietmar Eggemann , "H . Peter Anvin" , Ingo Molnar , Juri Lelli , Mel Gorman , Paolo Bonzini , Andy Lutomirski , Peter Zijlstra , Thomas Gleixner , Valentin Schneider , Vincent Guittot , Vitaly Kuznetsov , Wanpeng Li , Steven Rostedt , Suleiman Souhlal , Masami Hiramatsu , himadrics@inria.fr, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org, graf@amazon.com, drjunior.org@gmail.com References: <20240403140116.3002809-1-vineeth@bitbyteword.org> <66912820.050a0220.15d64.10f5@mx.google.com> <19ecf8c8-d5ac-4cfb-a650-cf072ced81ce@efficios.com> From: Mathieu Desnoyers Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 2024-07-12 12:24, Joel Fernandes wrote: > On Fri, Jul 12, 2024 at 10:09 AM Mathieu Desnoyers > wrote: [...] >>> >>> Steven Rostedt told me, what we instead need is a tracepoint callback in a >>> driver, that does the boosting. >> >> I utterly dislike changing the system behavior through tracepoints. They were >> designed to observe the system, not modify its behavior. If people start abusing >> them, then subsystem maintainers will stop adding them. Please don't do that. >> Add a notifier or think about integrating what you are planning to add into the >> driver instead. > > Well, we do have "raw" tracepoints not accessible from userspace, so > you're saying even those are off limits for adding callbacks? Yes. Even the "raw" tracepoints were designed as an "observation only" API. Using them in lieu of notifiers is really repurposing them for something they were not meant to do. Just in terms of maintainability at the caller site, we should be allowed to consider _all_ tracepoints as mostly exempt from side-effects outside of the data structures within the attached tracers. This is not true anymore if they are repurposed as notifiers. Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. https://www.efficios.com