From owner-freebsd-arch@FreeBSD.ORG Fri Feb 27 15:51:50 2015 Return-Path: Delivered-To: freebsd-arch@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id 58DDEF55 for ; Fri, 27 Feb 2015 15:51:50 +0000 (UTC) Received: from mailout.easymail.ca (mailout.easymail.ca [64.68.201.169]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 113D4D10 for ; Fri, 27 Feb 2015 15:51:49 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by mailout.easymail.ca (Postfix) with ESMTP id 3A920E3E2 for ; Fri, 27 Feb 2015 10:51:42 -0500 (EST) X-Virus-Scanned: Debian amavisd-new at mailout.easymail.ca X-Spam-Flag: NO X-Spam-Score: -3.855 X-Spam-Level: X-Spam-Status: No, score=-3.855 required=5 tests=[ALL_TRUSTED=-1.8, AWL=-0.148, BAYES_00=-2.599, DNS_FROM_AHBL_RHSBL=0.692] Received: from mailout.easymail.ca ([127.0.0.1]) by localhost (easymail-mailout.easydns.vpn [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id GIbWSYbD-8TH for ; Fri, 27 Feb 2015 10:51:42 -0500 (EST) Received: from bsddt1241.lv01.astrodoggroup.com (unknown [40.141.24.126]) (using TLSv1 with cipher DHE-RSA-AES128-SHA (128/128 bits)) (No client certificate requested) by mailout.easymail.ca (Postfix) with ESMTPSA id E02AEE3D9 for ; Fri, 27 Feb 2015 10:51:41 -0500 (EST) Message-ID: <54F0925F.30002@astrodoggroup.com> Date: Fri, 27 Feb 2015 07:50:55 -0800 From: Harrison Grundy User-Agent: Mozilla/5.0 (X11; FreeBSD amd64; rv:31.0) Gecko/20100101 Thunderbird/31.3.0 MIME-Version: 1.0 To: freebsd-arch@freebsd.org Subject: Re: Minor ULE changes and optimizations References: <54EF2C54.7030207@astrodoggroup.com> <2311645.BNIPBaFv2E@ralph.baldwin.cx> In-Reply-To: <2311645.BNIPBaFv2E@ralph.baldwin.cx> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 8bit X-BeenThere: freebsd-arch@freebsd.org X-Mailman-Version: 2.1.18-1 Precedence: list List-Id: Discussion related to FreeBSD architecture List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 27 Feb 2015 15:51:50 -0000 On 02/27/15 06:14, John Baldwin wrote: > On Thursday, February 26, 2015 06:23:16 AM Harrison Grundy wrote: >> https://reviews.freebsd.org/D1969 This allows a non-migratable >> thread to pin itself to a CPU if it is already running on that >> CPU. >> >> I've been running these patches for the past week or so without >> issue. Any additional testing or comments would be greatly >> appreciated. > > Can you explain the reason / use case for this? This seems to be > allowing an API violation. sched_pin() was designed to be a > lower-level API than sched_bind(), so you wouldn't call > sched_bind() if you were already pinned. In addition, sched_pin() > is sometimes used by code that assumes it won't migrate until > sched_unpin() (e.g. temporary mappings inside an sfbuf). If you > allow sched_bind() to move a thread that is pinned you will allow > someone to unintentionally break those sort of things instead of > getting an assertion failure panic. > For a pinned thread, the underlying idea is that if you're already on the CPU you pinned to, calling sched_bind with that CPU specified allows you to set TSF_BOUND without calling sched_unpin first. If a pinned thread were to call sched_bind for a CPU it isn't pinned to, it would still hit the assert and fail. For any unpinned thread, if you're already running on the correct CPU, you can skip the THREAD_CAN_MIGRATE check and the call to mi_switch. --- Harrison