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 A96B21F62E for ; Wed, 16 Jan 2019 15:33:11 +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:from:to:cc:subject:references:date:in-reply-to :message-id:mime-version:content-type; q=dns; s=default; b=BecnL gI/1Hkb9l+CyJKPWt5OxeEnZw+hfjEb3xktQY9SS8r6/l8VyvpFedkvULK2XqJ6z ITz3nZKNbeqnblA+31buC94beYWZSP71u03zYRoHxTL+Cc7iABZozEeAahxqUq7W qSn8nMg7pcA9cmbxpNFRwYZIlJnzIbu++rUeik= 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:from:to:cc:subject:references:date:in-reply-to :message-id:mime-version:content-type; s=default; bh=shQPFVlRuh1 79daOoX/LfJ9ZjmM=; b=j+HcdprmPdbAbotLiaG3g36AFRLAUugCQeR/JIZdyni BxRoxnca2K72fFcx5khpleqkxlvEki8h08pEhMuYFwnpzpJAI96gNLbDfkz01Mkm QCQBXgkuoGtUFMvZStRSY81742MhbIrwoY5dyNiAFFGKauEywEBkYgeFJg6QAe2s = Received: (qmail 109068 invoked by alias); 16 Jan 2019 15:33:09 -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 109051 invoked by uid 89); 16 Jan 2019 15:33:08 -0000 Authentication-Results: sourceware.org; auth=none X-HELO: mx1.redhat.com From: Florian Weimer To: Carlos O'Donell Cc: libc-alpha@sourceware.org Subject: Re: [PATCH] malloc: Revert fastbins to old-style atomics References: <87d0owzrcf.fsf@oldenburg2.str.redhat.com> <793fa38d-e8aa-4903-5dfd-7997d511c367@redhat.com> Date: Wed, 16 Jan 2019 16:33:03 +0100 In-Reply-To: <793fa38d-e8aa-4903-5dfd-7997d511c367@redhat.com> (Carlos O'Donell's message of "Wed, 16 Jan 2019 10:18:54 -0500") Message-ID: <87k1j4wrbk.fsf@oldenburg2.str.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain * Carlos O'Donell: > 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? The other thread is here: Thanks, Florian