From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [216.205.24.124]) by sourceware.org (Postfix) with ESMTP id 89C0D385700A for ; Thu, 14 Jan 2021 12:54:15 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 89C0D385700A Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-257-YhoSh5gfPFqyqxYU75GHow-1; Thu, 14 Jan 2021 07:54:11 -0500 X-MC-Unique: YhoSh5gfPFqyqxYU75GHow-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 440D69CC03; Thu, 14 Jan 2021 12:54:10 +0000 (UTC) Received: from localhost (unknown [10.33.37.44]) by smtp.corp.redhat.com (Postfix) with ESMTP id C16FB19C47; Thu, 14 Jan 2021 12:54:09 +0000 (UTC) Date: Thu, 14 Jan 2021 12:54:08 +0000 From: Jonathan Wakely To: Alexandre Oliva Cc: libstdc++@gcc.gnu.org, gcc-patches@gcc.gnu.org Subject: Re: calibrate intervals to avoid zero in futures poll test Message-ID: <20210114125408.GA7692@redhat.com> References: MIME-Version: 1.0 In-Reply-To: X-Clacks-Overhead: GNU Terry Pratchett X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline X-Spam-Status: No, score=-14.6 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, RCVD_IN_DNSWL_LOW, RCVD_IN_MSPIKE_H3, RCVD_IN_MSPIKE_WL, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.2 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on server2.sourceware.org X-BeenThere: gcc-patches@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 14 Jan 2021 12:54:17 -0000 On 05/01/21 04:44 -0300, Alexandre Oliva wrote: > >We get occasional failures of 30_threads/future/members/poll.cc >on some platforms whose high resolution clock doesn't have such a high >resolution; wait_for_0 ends up as 0, and then some asserts fail as >intervals measured as longer than zero are tested for less than >several times zero. > >This patch adds some calibration in the iteration count to set a >measurable base time interval with some additional margin. > >Regstrapped on x86_64-linux-gnu, and also tested on >x-arm-wrs-vxworks7r2. Ok to install? > > >for libstdc++-v3/ChangeLog > > * testsuite/30_threads/future/members/poll.cc: Calibrate > iteration count. >--- > .../testsuite/30_threads/future/members/poll.cc | 33 +++++++++++++++++++- > 1 file changed, 32 insertions(+), 1 deletion(-) > >diff --git a/libstdc++-v3/testsuite/30_threads/future/members/poll.cc b/libstdc++-v3/testsuite/30_threads/future/members/poll.cc >index fff9bea899c90..7b41411a54386 100644 >--- a/libstdc++-v3/testsuite/30_threads/future/members/poll.cc >+++ b/libstdc++-v3/testsuite/30_threads/future/members/poll.cc >@@ -25,7 +25,7 @@ > #include > #include > >-const int iterations = 200; >+int iterations = 200; > > using namespace std; > >@@ -45,10 +45,41 @@ int main() > promise p; > future f = p.get_future(); > >+ start_over: > auto start = chrono::high_resolution_clock::now(); > for(int i = 0; i < iterations; i++) > f.wait_for(chrono::seconds(0)); > auto stop = chrono::high_resolution_clock::now(); >+ >+ /* We've run too few iterations for the clock resolution. >+ Attempt to calibrate it. */ >+ if (start == stop) >+ { >+ /* Loop until the clock advances, so that start is right after a >+ time increment. */ >+ do >+ start = chrono::high_resolution_clock::now(); >+ while (start == stop); >+ int i = 0; >+ /* Now until the clock advances again, so that stop is right >+ after another time increment. */ >+ do >+ { >+ f.wait_for(chrono::seconds(0)); >+ stop = chrono::high_resolution_clock::now(); >+ i++; >+ } >+ while (start == stop); >+ /* Got for some 10 cycles, but we're already past that and still I can't parse "Got for some 10 cycles". If that's just a typo that I'm failing to spot ("good for"?) please fix and push the patch. The patch is fine apart from me being unable to understand this comment. >+ get into the calibration loop, double the iteration count and >+ try again. */ >+ if (iterations < i * 10) >+ iterations = i * 10; >+ else >+ iterations *= 2; >+ goto start_over; >+ } >+ > double wait_for_0 = print("wait_for(0s)", stop - start); > > start = chrono::high_resolution_clock::now(); > > >-- >Alexandre Oliva, happy hacker https://FSFLA.org/blogs/lxo/ > Free Software Activist GNU Toolchain Engineer > Vim, Vi, Voltei pro Emacs -- GNUlius Caesar >