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=-2.2 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,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 1F49FC43331 for ; Fri, 6 Sep 2019 17:07:37 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 E928620578 for ; Fri, 6 Sep 2019 17:07:36 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="TceU5N+1" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E928620578 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lst.de Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-riscv-bounces+infradead-linux-riscv=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=mZQTdYkVVq8qwvHe6gpX0z5ETuc0h7K9Y192zwHbk0k=; b=TceU5N+1m+iyvZ seC3cFjZezCN8DGHJ0XIe/gw/nIGE5wn5zRnjRoI5j3tx1k6v/GDyjOTi4NxKY6d+ZFofFkznyQhe CJGiyC943wo8JX0cmxTgRabyuAnOLA3JiNsNF6PKf00gnqmKVRTBLH8YDLJVQAWoFsW4yQabu8YH4 OKFvw56Nd7zPlOo7E+Z1WewwVggSxfIq2xf1/IJouoe0m9qB5JOToVwIWxTvW2rN/bf0hzLcwecPS Vg8oi6RanU2bZMkrrsXBVlxsCMEk78srrVkO5vHCaW01A9/w5K9g8BQ0JAWIf8d5fSIoP6OhTDR3K Ki930qa5S7Wi1fYdr4/Q==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1i6Hhu-0002ks-GO; Fri, 06 Sep 2019 17:07:34 +0000 Received: from verein.lst.de ([213.95.11.211]) by bombadil.infradead.org with esmtps (Exim 4.92 #3 (Red Hat Linux)) id 1i6Hhr-0002hj-5y for linux-riscv@lists.infradead.org; Fri, 06 Sep 2019 17:07:32 +0000 Received: by verein.lst.de (Postfix, from userid 2407) id 4390268B05; Fri, 6 Sep 2019 19:07:25 +0200 (CEST) Date: Fri, 6 Sep 2019 19:07:25 +0200 From: Christoph Hellwig To: Palmer Dabbelt Subject: Re: [PATCH 8/8] riscv: ignore the SYS_RISCV_FLUSH_ICACHE_LOCAL flag Message-ID: <20190906170725.GA13047@lst.de> References: <20190828060942.GA21592@lst.de> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190906_100731_368198_A0D2E333 X-CRM114-Status: GOOD ( 12.38 ) X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-riscv@lists.infradead.org, Christoph Hellwig , Paul Walmsley Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-riscv" Errors-To: linux-riscv-bounces+infradead-linux-riscv=archiver.kernel.org@lists.infradead.org On Tue, Sep 03, 2019 at 11:46:33AM -0700, Palmer Dabbelt wrote: > This is used by userspace as a thread-local icache barrier: there's an > immediate fence on the current hart, and one will be executed before that > thread makes it to userspace on another hart. As far as I can tell this is > implemented correctly but not optimally: there's always a fence, but we > emit an unnecessary fence when a different thread in the same context is > scheduled on a different hart. > > I suppose maybe we should attach the local fence mask to a task_struct > instead of an mm_struct, which would trade off an extra load in the > scheduler (to check both places) or more fences in the global case (on > every thread getting scheduled) for fewer fences in the local case. I feel > like it's not really worth worrying about this for now. > > The construct seems reasonable to me. I haven't been able to poke holes into that idea yet, but I'll try a bit more once I find a little time. _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv