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=-2.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,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 A16E3C3A5A8 for ; Wed, 4 Sep 2019 18:23:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7DB6422CEA for ; Wed, 4 Sep 2019 18:23:45 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="B68GhDH9" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388957AbfIDSXh (ORCPT ); Wed, 4 Sep 2019 14:23:37 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:56662 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388764AbfIDSCc (ORCPT ); Wed, 4 Sep 2019 14:02:32 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=YWE0H+jTpcN/XC6vFgWxU0Ifm430UGtAcUQBmeqFffU=; b=B68GhDH9ylcTgqElA2r7zjY7O lE6Rf0/LqJ/dbv7yx7jsCmrYsQoXzrSLpLhPKVcAq09WGGtdvjGxnz3fv+EJhtL7AFUeyL4hUtuyt SO8pIA93xdezldWmlYuoV9FK9U45Phywr2f2VSWHYoZWaGJ6vERLfLEyOxy6AI5yugAjiWfw2SeTE zbIU0h3IF2lpVTqWz7YPsRl3U0CE6wMNg2JLLw7DHSeFIaNu7K1T1oDbBlZnpyhAvdSKmvaSu5HCE Pl8vLB1RU4X/IesTI8jJ4p8o22IevZ5TrXbR/ihKRX90p+CdzzdIVoIQQjW6xLbRAVWLBZKQa/0ga ZRDX5wwYQ==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.92 #3 (Red Hat Linux)) id 1i5Zbi-0004qX-Oq; Wed, 04 Sep 2019 18:02:14 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 32C2D3060BF; Wed, 4 Sep 2019 20:01:35 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id CD686201265AF; Wed, 4 Sep 2019 20:02:11 +0200 (CEST) Date: Wed, 4 Sep 2019 20:02:11 +0200 From: Peter Zijlstra To: Bart Van Assche Cc: Daniel Lezcano , Ming Lei , Keith Busch , Hannes Reinecke , Sagi Grimberg , linux-scsi@vger.kernel.org, Long Li , John Garry , LKML , linux-nvme@lists.infradead.org, Jens Axboe , Ingo Molnar , Thomas Gleixner , Christoph Hellwig Subject: Re: [PATCH 1/4] softirq: implement IRQ flood detection mechanism Message-ID: <20190904180211.GX2332@hirez.programming.kicks-ass.net> References: <20190903033001.GB23861@ming.t460p> <299fb6b5-d414-2e71-1dd2-9d6e34ee1c79@linaro.org> <20190903063125.GA21022@ming.t460p> <6b88719c-782a-4a63-db9f-bf62734a7874@linaro.org> <20190903072848.GA22170@ming.t460p> <6f3b6557-1767-8c80-f786-1ea667179b39@acm.org> <2a8bd278-5384-d82f-c09b-4fce236d2d95@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-scsi-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-scsi@vger.kernel.org On Wed, Sep 04, 2019 at 10:38:59AM -0700, Bart Van Assche wrote: > On 9/4/19 10:31 AM, Daniel Lezcano wrote: > > On 04/09/2019 19:07, Bart Van Assche wrote: > > > Only if CONFIG_IRQ_TIME_ACCOUNTING has been enabled. However, I don't > > > know any Linux distro that enables that option. That's probably because > > > that option introduces two rdtsc() calls in each interrupt. Given the > > > overhead introduced by this option, I don't think this is the solution > > > Ming is looking for. > > > > Was this overhead reported somewhere ? > I think it is widely known that rdtsc is a relatively slow x86 instruction. > So I expect that using that instruction will cause a measurable overhead if > it is called frequently enough. I'm not aware of any publicly available > measurement data however. https://www.agner.org/optimize/instruction_tables.pdf RDTSC, Ryzen: ~36 RDTSC, Skylake: ~20 Sadly those same tables don't list the cost of actual exceptions or even IRET :/