From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 18557C33C9E for ; Sat, 11 Jan 2020 11:45:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E402A20842 for ; Sat, 11 Jan 2020 11:45:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729434AbgAKLo0 (ORCPT ); Sat, 11 Jan 2020 06:44:26 -0500 Received: from mx.sdf.org ([205.166.94.20]:50141 "EHLO mx.sdf.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728749AbgAKLoZ (ORCPT ); Sat, 11 Jan 2020 06:44:25 -0500 Received: from sdf.org (IDENT:lkml@sdf.lonestar.org [205.166.94.16]) by mx.sdf.org (8.15.2/8.14.5) with ESMTPS id 00BBi8iS024333 (using TLSv1.2 with cipher DHE-RSA-AES256-GCM-SHA384 (256 bits) verified NO); Sat, 11 Jan 2020 11:44:08 GMT Received: (from lkml@localhost) by sdf.org (8.15.2/8.12.8/Submit) id 00BBiXEq002960; Sat, 11 Jan 2020 11:44:33 GMT Date: Sat, 11 Jan 2020 11:44:33 GMT From: George Spelvin Message-Id: <202001111144.00BBiXEq002960@sdf.org> To: andy.shevchenko@gmail.com, keith.busch@intel.com, lkml@sdf.org Subject: Re: [PATCH] lib/list_sort: fix function type mismatches Cc: akpm@linux-foundation.org, andriy.shevchenko@linux.intel.com, keescook@chromium.org, linux-kernel@vger.kernel.org, linux@rasmusvillemoes.dk, mchehab+samsung@kernel.org, samitolvanen@google.com, st5pub@yandex.ru In-Reply-To: References: <20200110225602.91663-1-samitolvanen@google.com>, <202001110830.00B8USV0024843@sdf.org>, Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 11 Jan 2020 at 12:35, Andy Shevchenko wrote: > Hint: When you post Message-Id you may prefix them with > https://lore.kernel.org/r/ which makes search a bit more convenient > and faster. I just learned that https://marc.info/?i= also works, so https://lore.kernel.org/r/20191007135656.37734-1-andriy.shevchenko@linux.intel.com https://marc.info/?i=20191007135656.37734-1-andriy.shevchenko@linux.intel.com https://lore.kernel.org/r/20190416154522.65aaa348161fc581181b56d9@linux-foundation.org https://marc.info/?i=20190416154522.65aaa348161fc581181b56d9@linux-foundation.org > For the record, I have just checked users of list_sort() in regard to > constify of priv parameter and only ACPI HMAT is using it as not > const. UBIFS and XFS do not change the data (if I didn't miss > anything). Yes, that initiator_cmp() at drivers/acpi/hmat/hmat.c:526 is... interesting. Basically, it wants to fill in a bitmap of all of the processor_pxm identifiers, so it avoids having a separate list traversal by setting bits in the compare function (which is guaranteed to visit each list element at least once). It ends up setting each bit 2*log2(n) times (since there are an average of log2(n) compares per element and each compare sets two bits), but it makes the code smaller. And although it make the aggressive performance optimizer in me cringe, I have to agree this is not performance-critical code and so it's a reasonable thing to do. I do note, however, that the list_sort is almost immediately followed by a list_for_each_entry() loop and maybe the bitmap computation could be folded in there. Basically start the loop with: unsigned int pxm = -1u; /* Invalid sentinel value */ list_for_each_entry(initiator, &initiators, node) { u32 value; if (initiator->processor_pxm != pxm) { pxm = initiator->processor_pxm; set_bit(pxm, p_nodes); } else if (!test_bit(pxm, p_nodes)) { continue; } ... but oh, whoops, that won't work. The "almost immediately" glosses over a second loop, so there are multiple passes over the initiators list, while we want the bitmap set up only once. Cc: to Keith Busch , who wrote that code. Keith, is there a way we could avoid the non-const priv parameter, just for the sake of code cleanliness in ?