From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on dcvr.yhbt.net X-Spam-Level: X-Spam-ASN: AS31976 209.132.180.0/23 X-Spam-Status: No, score=-4.0 required=3.0 tests=AWL,BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_EF,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RCVD_IN_DNSWL_MED,SPF_HELO_PASS,SPF_PASS shortcircuit=no autolearn=ham autolearn_force=no version=3.4.2 Received: from sourceware.org (server1.sourceware.org [209.132.180.131]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dcvr.yhbt.net (Postfix) with ESMTPS id 9082F211B4 for ; Wed, 16 Jan 2019 15:19:03 +0000 (UTC) DomainKey-Signature: a=rsa-sha1; c=nofws; d=sourceware.org; h=list-id :list-unsubscribe:list-subscribe:list-archive:list-post :list-help:sender:subject:to:references:from:message-id:date :mime-version:in-reply-to:content-type :content-transfer-encoding; q=dns; s=default; b=rE2hmj0pMJjJPkQg aeL7XGBKWULtYBWl4eeKfRhkAG0YZ9Cm5EAeJftOmrOInaaaL42NENZT1z1GKl8A lRKSCJHWYkNeomxd0a8C1PDanrj1hUQ5PDus95K2NcTIR+575d54iemMiLo9VJtO 9+I8bZXiEfek5wcPZSu08rLwiV4= DKIM-Signature: v=1; a=rsa-sha1; c=relaxed; d=sourceware.org; h=list-id :list-unsubscribe:list-subscribe:list-archive:list-post :list-help:sender:subject:to:references:from:message-id:date :mime-version:in-reply-to:content-type :content-transfer-encoding; s=default; bh=omovF7DsSXbn3zMtSMUohq JVTC8=; b=DcBfsOLzqnMxunwkr5Lve/sQhXZNBdg2N1c2dDGR0dSoZqJjVFeF66 rQcyKudOijdXhwuoVJ79uDgXWTJ+jxP2YA9i4f7Wav3/jyE+PDr5itnCSE1v9GFO 1xYt1Dwnq7NmR+FWI3i8ShJKxfVk7+qt5sXfjdJcdTrCVym4b1AaI= Received: (qmail 58503 invoked by alias); 16 Jan 2019 15:19:01 -0000 Mailing-List: contact libc-alpha-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Unsubscribe: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: libc-alpha-owner@sourceware.org Received: (qmail 58465 invoked by uid 89); 16 Jan 2019 15:19:00 -0000 Authentication-Results: sourceware.org; auth=none X-HELO: mail-qt1-f194.google.com Subject: Re: [PATCH] malloc: Revert fastbins to old-style atomics To: Florian Weimer , libc-alpha@sourceware.org References: <87d0owzrcf.fsf@oldenburg2.str.redhat.com> From: Carlos O'Donell Openpgp: preference=signencrypt Message-ID: <793fa38d-e8aa-4903-5dfd-7997d511c367@redhat.com> Date: Wed, 16 Jan 2019 10:18:54 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: <87d0owzrcf.fsf@oldenburg2.str.redhat.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit On 1/16/19 8:04 AM, Florian Weimer wrote: > Commit 6923f6db1e688dedcf3a6556da76e0bf24a41872 ("malloc: Use current > (C11-style) atomics for fastbin access") caused a substantial > performance regression on POWER and Aarch64, and the old atomics, > while hard to prove correct, seem to work in practice. Why is it slow? What do the benchmarks say? What does profiling show to be the slow instruction? How is the instruction sequence different from before that causes the problem? -- Cheers, Carlos.