From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.1 (2015-04-28) on archive.lwn.net X-Spam-Level: X-Spam-Status: No, score=-4.8 required=5.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, RCVD_IN_DNSWL_HI,T_RP_MATCHES_RCVD autolearn=ham autolearn_force=no version=3.4.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by archive.lwn.net (Postfix) with ESMTP id 3F92E7E22E for ; Mon, 2 Apr 2018 08:18:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754324AbeDBISl (ORCPT ); Mon, 2 Apr 2018 04:18:41 -0400 Received: from exmail.andestech.com ([59.124.169.137]:51455 "EHLO ATCSQR.andestech.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754139AbeDBISl (ORCPT ); Mon, 2 Apr 2018 04:18:41 -0400 Received: from mail.andestech.com (atcpcs16.andestech.com [10.0.1.222]) by ATCSQR.andestech.com with ESMTP id w328D3Iv059149; Mon, 2 Apr 2018 16:13:03 +0800 (GMT-8) (envelope-from alankao@andestech.com) Received: from andestech.com (10.0.1.85) by ATCPCS16.andestech.com (10.0.1.222) with Microsoft SMTP Server id 14.3.123.3; Mon, 2 Apr 2018 16:18:05 +0800 Date: Mon, 2 Apr 2018 16:18:06 +0800 From: Alan Kao To: Alex Solomatnikov CC: Nick Hu , Jonathan Corbet , "Peter Zijlstra" , Palmer Dabbelt , , , "Arnaldo Carvalho de Melo" , Alexander Shishkin , Ingo Molnar , "Albert Ou" , Namhyung Kim , , Jiri Olsa , Greentime Hu Subject: Re: [PATCH 1/2] perf: riscv: preliminary RISC-V support Message-ID: <20180402081806.GA24954@andestech.com> References: <1522051075-6442-1-git-send-email-alankao@andestech.com> <1522051075-6442-2-git-send-email-alankao@andestech.com> <20180329023024.GA32659@andestech.com> <20180402073611.GA7694@andestech.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20180402073611.GA7694@andestech.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Originating-IP: [10.0.1.85] X-DNSRBL: X-MAIL: ATCSQR.andestech.com w328D3Iv059149 Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org Hi Alex, On Mon, Apr 02, 2018 at 03:36:12PM +0800, Alan Kao wrote: > On Sat, Mar 31, 2018 at 03:47:10PM -0700, Alex Solomatnikov wrote: > > The original guess was that maybe, an counter value on a hart is picked > as the minusend, and an old counter value on another hart was recorded > as the subtrahend but numerically larger. Then, the overflow causes > by that subtraction. Please let me name this guess as > "cross-hart subtraction." > > > You can add a skew between cores in qemu, something like this: > > > > case CSR_INSTRET: > > core_id()*return cpu_get_host_ticks()/10; > > break; > > case CSR_CYCLE: > > return cpu_get_host_ticks(); > > break; > > > > However, I tried similar stuff to reproduce the phenomenon but in vain. > It seems that the > > ***cross-hart subtration doesn't even happen, because generic > code handles them. ... I am sorry that this observation is wrong. With appropriate tweak, we successfully reproduce the behavior and locate the the bug. This will be fix in v2. Thanks for the helps. Alan -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html