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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham 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 C1234C4360F for ; Fri, 5 Apr 2019 11:09:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9928F2171F for ; Fri, 5 Apr 2019 11:09:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730780AbfDELJC (ORCPT ); Fri, 5 Apr 2019 07:09:02 -0400 Received: from mx1.redhat.com ([209.132.183.28]:57516 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730497AbfDELJC (ORCPT ); Fri, 5 Apr 2019 07:09:02 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 21BB489C47; Fri, 5 Apr 2019 11:09:02 +0000 (UTC) Received: from oldenburg2.str.redhat.com (ovpn-116-233.ams2.redhat.com [10.36.116.233]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 9999A5D707; Fri, 5 Apr 2019 11:09:00 +0000 (UTC) From: Florian Weimer To: Peter Zijlstra Cc: Alexey Dobriyan , mingo@redhat.com, linux-kernel@vger.kernel.org, linux-api@vger.kernel.org Subject: Re: [PATCH] sched/core: expand sched_getaffinity(2) to return number of CPUs References: <20190403200809.GA13876@avx2> <20190404084249.GS4038@hirez.programming.kicks-ass.net> <87wok83gfs.fsf@oldenburg2.str.redhat.com> <20190405110415.GP12232@hirez.programming.kicks-ass.net> Date: Fri, 05 Apr 2019 13:08:58 +0200 In-Reply-To: <20190405110415.GP12232@hirez.programming.kicks-ass.net> (Peter Zijlstra's message of "Fri, 5 Apr 2019 13:04:15 +0200") Message-ID: <87ftqw3e0l.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 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.27]); Fri, 05 Apr 2019 11:09:02 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Peter Zijlstra: > On Fri, Apr 05, 2019 at 12:16:39PM +0200, Florian Weimer wrote: > >> > True; but I suppose glibc already does lots of that anyway, right? It >> > does contain the right information. >> >> If I recall correctly my last investigation, >> /sys/devices/system/cpu/possible does not reflect the size of the >> affinity mask, either. > > Strictly speaking correct; the bitmap can be longer than the highest > possible cpu number, however the remainder would be 0-padding and could > thus be stripped without issue. Doesn't the kernel still enforce the larget bitmap in sched_getaffinity, even if the bits are always zero? Thanks, Florian