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-Status: No, score=-3.7 required=3.0 tests=AWL,BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS shortcircuit=no autolearn=ham autolearn_force=no version=3.4.2 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by dcvr.yhbt.net (Postfix) with ESMTP id 48FDC1F66E for ; Fri, 21 Aug 2020 18:09:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726906AbgHUSJN (ORCPT ); Fri, 21 Aug 2020 14:09:13 -0400 Received: from mail-ed1-f66.google.com ([209.85.208.66]:33547 "EHLO mail-ed1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725885AbgHUSJI (ORCPT ); Fri, 21 Aug 2020 14:09:08 -0400 Received: by mail-ed1-f66.google.com with SMTP id w14so1683238eds.0 for ; Fri, 21 Aug 2020 11:09:07 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=J9h3sOBY/Tck6Db07/JOSoMRB1VHPGjHp+Qupte7AHc=; b=LgEPDPkplaGG23eic0L94ZdjtmzSnwkOOBUUkFDacBTlW8pdB3tAs6RSdGUS3opHG0 i1gODNjsgBUGXUgUJalrP05oATyHSRyUMCbby7Pdn4gzWgJcQPlrAGsCunaCgwikKzXa d4Y56a09yOg5xJX5YUDNxiVgqH47vTOoKHpQ24BENBV+rmt1wrWrPBb5g0pTpPB3gXeJ duj9567rTA4LFnuXInOeLaJeOJiuf8omW5fDgOD9d5vye7omZdZzsjFVNqX1oxzpkmF9 u5j/Ywr+6uJzS1ewV97MQHd9v2C4NOPpIN/n2HgKDJh+VAGwWUvtESKAwOZIZcpXO02/ /yIQ== X-Gm-Message-State: AOAM533w//9OLVfEltFz271gLHk0+rF7vvjGkcysWjIfG11O59c4G8Ui CRmhYJVctRUZ9oWPfNVNntEKQWg42LTW9eeF+1mFSI8K X-Google-Smtp-Source: ABdhPJxdDu3nEOa7aG6p32EQBhU4xXWllKGMo+Lmx1H/yS40UAtVrMib+ZSWo52QrcBGeBtFBAmY2srWJsJV/q1w3qo= X-Received: by 2002:a50:8f85:: with SMTP id y5mr4082864edy.233.1598033346615; Fri, 21 Aug 2020 11:09:06 -0700 (PDT) MIME-Version: 1.0 References: <20200821175153.GA3263018@coredump.intra.peff.net> <20200821175800.GC3263141@coredump.intra.peff.net> In-Reply-To: <20200821175800.GC3263141@coredump.intra.peff.net> From: Eric Sunshine Date: Fri, 21 Aug 2020 14:08:55 -0400 Message-ID: Subject: Re: [PATCH 3/3] index-pack: adjust default threading cap To: Jeff King Cc: Git List Content-Type: text/plain; charset="UTF-8" Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org On Fri, Aug 21, 2020 at 1:58 PM Jeff King wrote: > So what's a good default value? It's clear that the current cap of 3 is > too low; our default values are 42% and 57% slower than the best times > on each machine. The results on the 40-core machine imply that 20 > threads is an actual barrier regardless of the number of cores, so we'll > take that as a maximum. We get the best results on these machines at > half of the online-cpus value. That's presumably a result of the > hyperthreading. That's common on multi-core Intel processors, but not > necessarily elsewhere. But if we take it as an assumption, we can > perform optimally on hyperthreaded machines and still do much better > than the status quo on other machines, as long as we never half below > the current value of 3. I'm not familiar with the index-pack machinery, so this response may be silly, but the first question which came to my mind was whether or not SSD vs. spinning-platter disk impacts these results, and which of the two you were using for the tests (which I don't think was mentioned in any of the commit messages). So, basically, I'm wondering about the implication of this change for those of us still stuck with old spinning-platter disks.