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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS 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 CA94AC433E0 for ; Tue, 26 Jan 2021 12:00:18 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 913972311C for ; Tue, 26 Jan 2021 12:00:17 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 913972311C Authentication-Results: mail.kernel.org; dmarc=pass (p=none dis=none) header.from=xenproject.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from list by lists.xenproject.org with outflank-mailman.74922.134736 (Exim 4.92) (envelope-from ) id 1l4N0o-0007Iy-CA; Tue, 26 Jan 2021 11:59:58 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 74922.134736; Tue, 26 Jan 2021 11:59:58 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1l4N0o-0007Ir-9D; Tue, 26 Jan 2021 11:59:58 +0000 Received: by outflank-mailman (input) for mailman id 74922; Tue, 26 Jan 2021 11:59:56 +0000 Received: from mail.xenproject.org ([104.130.215.37]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1l4N0m-0007Ii-JD for xen-devel@lists.xenproject.org; Tue, 26 Jan 2021 11:59:56 +0000 Received: from xenbits.xenproject.org ([104.239.192.120]) by mail.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1l4N0m-0005Ej-Fr for xen-devel@lists.xenproject.org; Tue, 26 Jan 2021 11:59:56 +0000 Received: from iwj (helo=mariner.uk.xensource.com) by xenbits.xenproject.org with local-bsmtp (Exim 4.92) (envelope-from ) id 1l4N0m-0000Nk-EI for xen-devel@lists.xenproject.org; Tue, 26 Jan 2021 11:59:56 +0000 Received: from iwj by mariner.uk.xensource.com with local (Exim 4.89) (envelope-from ) id 1l4N0j-0006Yb-9D; Tue, 26 Jan 2021 11:59:53 +0000 X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=xenproject.org; s=20200302mail; h=References:In-Reply-To:Subject:Cc:To:Date :Message-ID:Content-Transfer-Encoding:Content-Type:MIME-Version:From; bh=fyLcJUEl+vpyFvsICNx/DtSbC2DgOyWSN38osnP3qDs=; b=vm4sslkoBTGiKjzCyir28coJZw wjxNWwaJVDZSnw0vNqcQK+G4bfye2/K2CVHo2CaEsyozzxgSARdKhq9ia9fr4Mp6vWKSosrIlWroD EgyVkJEctwSX5qNBOJpq0jXoQnaDNB/MFRYzBluNO3qL4bWm59L0sB9NywyG8+m+GPfk=; From: Ian Jackson MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Message-ID: <24592.1081.38318.522643@mariner.uk.xensource.com> Date: Tue, 26 Jan 2021 11:59:53 +0000 To: Andrew Cooper Cc: Xen-devel , =?iso-8859-2?Q?Micha=B3_Leszczy=F1ski?= , Wei Liu , Tamas K Lengyel Subject: Re: [PATCH v7 08/10] tools/misc: Add xen-vmtrace tool In-Reply-To: References: <20210121212718.2441-1-andrew.cooper3@citrix.com> <20210121212718.2441-9-andrew.cooper3@citrix.com> <24586.61484.451595.44272@mariner.uk.xensource.com> X-Mailer: VM 8.2.0b under 24.5.1 (i686-pc-linux-gnu) Andrew Cooper writes ("Re: [PATCH v7 08/10] tools/misc: Add xen-vmtrace tool"): > On 22/01/2021 15:33, Ian Jackson wrote: > > Andrew Cooper writes ("[PATCH v7 08/10] tools/misc: Add xen-vmtrace tool"): > >> + if ( xc_vmtrace_disable(xch, domid, vcpu) ) > >> + perror("xc_vmtrace_disable()"); > > I guess the tracing will remain on, pointlessly, which has a perf > > impact but nothing else ? > > The perf hit is substantial, but it is safe to leave enabled. And how does one clean up after an unclean exit of this program ? > > How is it possible for the user to clean this up ? > > For now, enable/disable can only fail with -EINVAL for calls made in the > wrong context, so a failure here is benign in practice. > > I specifically didn't opt for reference counting the enable/disable > calls, because there cannot (usefully) be two users of this interface. Right. > > Also: at the very least, you need to trap SIGTERM SIGHUP SIGPIPE. > > > > It would be good to exit with the right signal by re-raising it. > > This is example code, not a production utility. Perhaps the utility could print some kind of health warning about it possibly leaving this perf-impacting feature enabled, and how to clean up ? Ian.