From mboxrd@z Thu Jan 1 00:00:00 1970 Received: with ECARTIS (v1.0.0; list linux-mips); Wed, 11 Jul 2018 12:16:56 +0200 (CEST) Received: from forward104p.mail.yandex.net ([77.88.28.107]:54796 "EHLO forward104p.mail.yandex.net" rhost-flags-OK-OK-OK-OK) by eddie.linux-mips.org with ESMTP id S23993514AbeGKKQuL4no4 convert rfc822-to-8bit (ORCPT ); Wed, 11 Jul 2018 12:16:50 +0200 Received: from mxback1g.mail.yandex.net (mxback1g.mail.yandex.net [IPv6:2a02:6b8:0:1472:2741:0:8b7:162]) by forward104p.mail.yandex.net (Yandex) with ESMTP id B3C52181BC3; Wed, 11 Jul 2018 13:14:57 +0300 (MSK) Received: from smtp3p.mail.yandex.net (smtp3p.mail.yandex.net [2a02:6b8:0:1472:2741:0:8b6:8]) by mxback1g.mail.yandex.net (nwsmtp/Yandex) with ESMTP id QIlY3WS5VM-Eu1G4nPP; Wed, 11 Jul 2018 13:14:57 +0300 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=flygoat.com; s=mail; t=1531304097; bh=XCCe7vZc7GQyW/Uk20RcYER7XQFfgxW8goHDS9VObxA=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References; b=WbgbahD0+vZJfY3jnRlpGa+xI1+WC81hJZdXBnPchpOduLhpn/jZRvMAZ+8rW8vpI KOxfFiGvAOvK9jE9PkbZQ6A4SsUnLCQRSLyy94R808f93VSpN5JhTiPtoU32YX/9dC 9tEgueIFzhdbbd6/DnLpi4KmciYvZ7xscM/3BOHM= Received: by smtp3p.mail.yandex.net (nwsmtp/Yandex) with ESMTPSA id fDNQFekDBA-EmhCeUUh; Wed, 11 Jul 2018 13:14:53 +0300 (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (Client certificate not present) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=flygoat.com; s=mail; t=1531304094; bh=XCCe7vZc7GQyW/Uk20RcYER7XQFfgxW8goHDS9VObxA=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References; b=eCSIkuGGxcPhycRObxIrrwZk4lN1sPuTvO3aqvHXxpZvZefNyJllo4kHv+gkw4dh+ RWbHVp4cBjBxmrYVpnHRPUW6P7P6Zs1xWkn2pgQKiQWB8D75meSOpG0ByfSFOICrVf XwXcAzmMoqMNG+zMQKj0C/EXrL2VcvzYeHMdgeRY= Authentication-Results: smtp3p.mail.yandex.net; dkim=pass header.i=@flygoat.com From: Jiaxun Yang To: linux-mips@linux-mips.org Cc: Peter Zijlstra , =?utf-8?B?6ZmI5Y2O5omN?= , Paul Burton , Ralf Baechle , James Hogan , Fuxin Zhang , wuzhangjin , stable , Alan Stern , Andrea Parri , Will Deacon , Boqun Feng , Nicholas Piggin , David Howells , Jade Alglave , Luc Maranget , "Paul E. McKenney" , Akira Yokosawa , LKML Subject: Re: [PATCH V2] MIPS: implement smp_cond_load_acquire() for Loongson-3 Date: Wed, 11 Jul 2018 18:05:51 +0800 Message-ID: <5471216.FKXZRxKFUI@flygoat-ry> In-Reply-To: <20180710121727.GK2476@hirez.programming.kicks-ass.net> References: <1531103198-16764-1-git-send-email-chenhc@lemote.com> <20180710121727.GK2476@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Transfer-Encoding: 8BIT Content-Type: text/plain; charset="UTF-8" Return-Path: X-Envelope-To: <"|/home/ecartis/ecartis -s linux-mips"> (uid 0) X-Orcpt: rfc822;linux-mips@linux-mips.org Original-Recipient: rfc822;linux-mips@linux-mips.org X-archive-position: 64778 X-ecartis-version: Ecartis v1.0.0 Sender: linux-mips-bounce@linux-mips.org Errors-to: linux-mips-bounce@linux-mips.org X-original-sender: jiaxun.yang@flygoat.com Precedence: bulk List-help: List-unsubscribe: List-software: Ecartis version 1.0.0 List-Id: linux-mips X-List-ID: linux-mips List-subscribe: List-owner: List-post: List-archive: X-list: linux-mips On 2018-7-10 Tue at 20:17:27，Peter Zijlstra Wrote： Hi Peter Since Huacai unable to send email via client, I'm going to reply for him > Sure.. we all got that far. And no, this isn't the _real_ problem. This > is a manifestation of the problem. > > The problem is that your SFB is broken (per the Linux requirements). We > require that stores will become visible. That is, they must not > indefinitely (for whatever reason) stay in the store buffer. > > > I don't think this is a hardware bug, in design, SFB will flushed to > > L1 cache in three cases: > > > > 1, data in SFB is full (be a complete cache line); > > 2, there is a subsequent read access in the same cache line; > > 3, a 'sync' instruction is executed. > > And I think this _is_ a hardware bug. You just designed the bug instead > of it being by accident. Yes, we understood that this hardware feature is not supported by LKML, so it should be a hardware bug for LKML. > > It doesn't happen an _any_ other architecture except that dodgy > ARM11MPCore part. Linux hard relies on stores to become available > _eventually_. > > Still, even with the rules above, the best work-around is still the very > same cpu_relax() hack. As you say, SFB makes Loongson not fully SMP-coherent. However, modify cpu_relax can solve the current problem, but not so straight forward. On the other hand, providing a Loongson-specific WRITE_ONCE looks more reasonable, because it the eliminate the "non-cohrency". So we can solve the bug from the root. Thanks. -- Jiaxun Yang