From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pj1-x102a.google.com (mail-pj1-x102a.google.com [IPv6:2607:f8b0:4864:20::102a]) by sourceware.org (Postfix) with ESMTPS id C70E53858401 for ; Sat, 6 Nov 2021 18:21:57 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org C70E53858401 Received: by mail-pj1-x102a.google.com with SMTP id gx15-20020a17090b124f00b001a695f3734aso5682019pjb.0 for ; Sat, 06 Nov 2021 11:21:57 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=mNtAxLAfGG/7nVPJbsVpmsDDOpGK5Fa9JX6Imp31/xo=; b=gCB/UZztDOm/YH0+fejGns8HvunzAyHAo14dd4r6ijPPS0MDPT70DdsmMaLspjIuGj 8NqI8xorvZj1BXi41vMdnLZkuaatj1VR6BmKvirm6CgA0PaaSqopvDcKlZhb0gPDTejI 1uYRtQ+6VRs4HQi6zyttnSR/PRtto/a6iJzISqQt3k7EPzPF0EEBcXFUauZRjbsSPYca Kz/eEXmP3zAmDN1tUZC2ewUjFDPpGQPJmyFUzPHox5z9Z9gkT+f+GjzZq/8DZVuL/HbV H20vDyLAwCvyFiLJ7adjBJ3/2QRAva0EhxsYXTLsLJfrW9MVmMMDoykFmihVfiaI2lsn hcTg== X-Gm-Message-State: AOAM533DhVALaA3k5yrduHkqmmDP8Y6JNjZd5kPnDjdJ41W+yDdesoun Tl/wuJ/88UIiyebVxPCzuK5OkHXqyOJjVzW0qJQ= X-Google-Smtp-Source: ABdhPJzU0s5qZzNg6vKG5cJy8klff4KdEjTPLGVW78/rgpX8dLs8aK5cJ3dIawBHJ2M4vDm4H5tuaGlwxrpS0MSaUQ4= X-Received: by 2002:a17:90a:9292:: with SMTP id n18mr39103886pjo.120.1636222916907; Sat, 06 Nov 2021 11:21:56 -0700 (PDT) MIME-Version: 1.0 References: <20211101054952.2349590-1-goldstein.w.n@gmail.com> <20211106173706.3125357-1-goldstein.w.n@gmail.com> <20211106173706.3125357-5-goldstein.w.n@gmail.com> In-Reply-To: From: "H.J. Lu" Date: Sat, 6 Nov 2021 11:21:21 -0700 Message-ID: Subject: Re: [PATCH v3 5/5] x86: Double size of ERMS rep_movsb_threshold in dl-cacheinfo.h To: Noah Goldstein Cc: GNU C Library Content-Type: text/plain; charset="UTF-8" X-Spam-Status: No, score=-3029.5 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, FREEMAIL_FROM, GIT_PATCH_0, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 06 Nov 2021 18:22:00 -0000 On Sat, Nov 6, 2021 at 11:12 AM Noah Goldstein wrote: > > On Sat, Nov 6, 2021 at 12:57 PM H.J. Lu wrote: > > > > On Sat, Nov 6, 2021 at 10:39 AM Noah Goldstein via Libc-alpha > > wrote: > > > > > > No bug. > > > > > > This patch doubles the rep_movsb_threshold when using ERMS. Based on > > > benchmarks the vector copy loop, especially now that it handles 4k > > > aliasing, is better for these medium ranged. > > > > > > On Skylake with ERMS: > > > > > > Size, Align1, Align2, dst>src,(rep movsb) / (vec copy) > > > 4096, 0, 0, 0, 0.975 > > > 4096, 0, 0, 1, 0.953 > > > 4096, 12, 0, 0, 0.969 > > > 4096, 12, 0, 1, 0.872 > > > 4096, 44, 0, 0, 0.979 > > > 4096, 44, 0, 1, 0.83 > > > 4096, 0, 12, 0, 1.006 > > > 4096, 0, 12, 1, 0.989 > > > 4096, 0, 44, 0, 0.739 > > > 4096, 0, 44, 1, 0.942 > > > 4096, 12, 12, 0, 1.009 > > > 4096, 12, 12, 1, 0.973 > > > 4096, 44, 44, 0, 0.791 > > > 4096, 44, 44, 1, 0.961 > > > 4096, 2048, 0, 0, 0.978 > > > 4096, 2048, 0, 1, 0.951 > > > 4096, 2060, 0, 0, 0.986 > > > 4096, 2060, 0, 1, 0.963 > > > 4096, 2048, 12, 0, 0.971 > > > 4096, 2048, 12, 1, 0.941 > > > 4096, 2060, 12, 0, 0.977 > > > 4096, 2060, 12, 1, 0.949 > > > 8192, 0, 0, 0, 0.85 > > > 8192, 0, 0, 1, 0.845 > > > 8192, 13, 0, 0, 0.937 > > > 8192, 13, 0, 1, 0.939 > > > 8192, 45, 0, 0, 0.932 > > > 8192, 45, 0, 1, 0.927 > > > 8192, 0, 13, 0, 0.621 > > > 8192, 0, 13, 1, 0.62 > > > 8192, 0, 45, 0, 0.53 > > > 8192, 0, 45, 1, 0.516 > > > 8192, 13, 13, 0, 0.664 > > > 8192, 13, 13, 1, 0.659 > > > 8192, 45, 45, 0, 0.593 > > > 8192, 45, 45, 1, 0.575 > > > 8192, 2048, 0, 0, 0.854 > > > 8192, 2048, 0, 1, 0.834 > > > 8192, 2061, 0, 0, 0.863 > > > 8192, 2061, 0, 1, 0.857 > > > 8192, 2048, 13, 0, 0.63 > > > 8192, 2048, 13, 1, 0.629 > > > 8192, 2061, 13, 0, 0.627 > > > 8192, 2061, 13, 1, 0.62 > > > --- > > > sysdeps/x86/dl-cacheinfo.h | 8 ++++---- > > > 1 file changed, 4 insertions(+), 4 deletions(-) > > > > > > diff --git a/sysdeps/x86/dl-cacheinfo.h b/sysdeps/x86/dl-cacheinfo.h > > > index e6c94dfd02..ceb3b53828 100644 > > > --- a/sysdeps/x86/dl-cacheinfo.h > > > +++ b/sysdeps/x86/dl-cacheinfo.h > > > @@ -866,12 +866,12 @@ dl_init_cacheinfo (struct cpu_features *cpu_features) > > > /* NB: The REP MOVSB threshold must be greater than VEC_SIZE * 8. */ > > > unsigned int minimum_rep_movsb_threshold; > > > #endif > > > - /* NB: The default REP MOVSB threshold is 2048 * (VEC_SIZE / 16). */ > > > + /* NB: The default REP MOVSB threshold is 4096 * (VEC_SIZE / 16). */ > > > unsigned int rep_movsb_threshold; > > > if (CPU_FEATURE_USABLE_P (cpu_features, AVX512F) > > > && !CPU_FEATURE_PREFERRED_P (cpu_features, Prefer_No_AVX512)) > > > { > > > - rep_movsb_threshold = 2048 * (64 / 16); > > > + rep_movsb_threshold = 4096 * (64 / 16); > > > #if HAVE_TUNABLES > > > minimum_rep_movsb_threshold = 64 * 8; > > > #endif > > > @@ -879,14 +879,14 @@ dl_init_cacheinfo (struct cpu_features *cpu_features) > > > else if (CPU_FEATURE_PREFERRED_P (cpu_features, > > > AVX_Fast_Unaligned_Load)) > > > { > > > - rep_movsb_threshold = 2048 * (32 / 16); > > > + rep_movsb_threshold = 4096 * (32 / 16); > > > #if HAVE_TUNABLES > > > minimum_rep_movsb_threshold = 32 * 8; > > > #endif > > > } > > > else > > > { > > > - rep_movsb_threshold = 2048 * (16 / 16); > > > + rep_movsb_threshold = 4096 * (16 / 16); > > > #if HAVE_TUNABLES > > > minimum_rep_movsb_threshold = 16 * 8; > > > #endif > > > -- > > > 2.25.1 > > > > > > > You need to update comments for x86_rep_movsb_threshold > > in sysdeps/x86/dl-tunables.list > > Can do. > > Noticing that the original values were based on comparisons with SSE2 likely on > SnB or IVB. I don't have any indication that the 2048 value is not > optimal for those > processors. Should we keep 2048 / (VEC_SIZE / 16) for SSE2? Good idea. So change the threshold to 2048 * (VEC_SIZE / 16) * (VEC_SIZE / 16)? -- H.J.