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=-0.9 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, URIBL_BLOCKED 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 1FDE8ECDE30 for ; Wed, 17 Oct 2018 15:11:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D81502150D for ; Wed, 17 Oct 2018 15:11:43 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=efficios.com header.i=@efficios.com header.b="IoEOgIuf" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D81502150D Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=efficios.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727835AbeJQXHu (ORCPT ); Wed, 17 Oct 2018 19:07:50 -0400 Received: from mail.efficios.com ([167.114.142.138]:57802 "EHLO mail.efficios.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727014AbeJQXHt (ORCPT ); Wed, 17 Oct 2018 19:07:49 -0400 Received: from localhost (ip6-localhost [IPv6:::1]) by mail.efficios.com (Postfix) with ESMTP id 1EC0A1CA6B4; Wed, 17 Oct 2018 11:11:41 -0400 (EDT) Received: from mail.efficios.com ([IPv6:::1]) by localhost (mail02.efficios.com [IPv6:::1]) (amavisd-new, port 10032) with ESMTP id 3t3An6xl9U90; Wed, 17 Oct 2018 11:11:40 -0400 (EDT) Received: from localhost (ip6-localhost [IPv6:::1]) by mail.efficios.com (Postfix) with ESMTP id 8E4CF1CA6AD; Wed, 17 Oct 2018 11:11:40 -0400 (EDT) DKIM-Filter: OpenDKIM Filter v2.10.3 mail.efficios.com 8E4CF1CA6AD DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=efficios.com; s=default; t=1539789100; bh=pOsEDiQXaRkGMm76xjqtw5SniO690HLscXPdPt3k9L8=; h=Date:From:To:Message-ID:MIME-Version; b=IoEOgIufWUIe0IYeoGBWoWN1oYlKlsfMTxhrs1qXRKLCcu1nbPMrt7kbFw8+pHrlY R56HLITNW/l3MJCDRDCs5qngBfkswSvKKJ3pMGp/s2tYKxaaaXj7ITdKxrhsYY97ZB q1ToqfinlxHNumfzhBRQDgU4UVnVNxYm5otmgOVTr1Kjc6OMb6t73hH7MFwMAVpWPb bTtiSM1nwuojshUz/i3qTNdwUIwVwoZKodZqGQizVHGQiJirUehRaTckMnDcGPX4l3 P7qCqS7NZf/2ZlEYAzeG72Ral1ATaeyn5f7jWwcsr1oFQNDaD29+TG2VDPF9dZdYww a/ymbrLOlJWnQ== X-Virus-Scanned: amavisd-new at efficios.com Received: from mail.efficios.com ([IPv6:::1]) by localhost (mail02.efficios.com [IPv6:::1]) (amavisd-new, port 10026) with ESMTP id m0gjQxnKcsKy; Wed, 17 Oct 2018 11:11:40 -0400 (EDT) Received: from mail02.efficios.com (mail02.efficios.com [167.114.142.138]) by mail.efficios.com (Postfix) with ESMTP id 6E04D1CA6A6; Wed, 17 Oct 2018 11:11:40 -0400 (EDT) Date: Wed, 17 Oct 2018 11:11:40 -0400 (EDT) From: Mathieu Desnoyers To: Srikar Dronamraju Cc: Peter Zijlstra , "Paul E. McKenney" , Boqun Feng , linux-kernel , linux-api , Thomas Gleixner , Andy Lutomirski , Dave Watson , Paul Turner , Andrew Morton , Russell King , Ingo Molnar , "H. Peter Anvin" , Andi Kleen , Chris Lameter , Ben Maurer , rostedt , Josh Triplett , Linus Torvalds , Catalin Marinas , Will Deacon , Michael Kerrisk , Joel Fernandes Message-ID: <1006597066.825.1539789100381.JavaMail.zimbra@efficios.com> In-Reply-To: <20181017071931.GA18379@linux.vnet.ibm.com> References: <20181010191936.7495-1-mathieu.desnoyers@efficios.com> <20181010191936.7495-7-mathieu.desnoyers@efficios.com> <20181017071931.GA18379@linux.vnet.ibm.com> Subject: Re: [RFC PATCH for 4.21 06/16] cpu_opv: Provide cpu_opv system call (v8) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Originating-IP: [167.114.142.138] X-Mailer: Zimbra 8.8.10_GA_3039 (ZimbraWebClient - FF52 (Linux)/8.8.10_GA_3041) Thread-Topic: cpu_opv: Provide cpu_opv system call (v8) Thread-Index: 7qW2lzGCTO+IxFmqU0Kf5LalV47JZQ== Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ----- On Oct 17, 2018, at 3:19 AM, Srikar Dronamraju srikar@linux.vnet.ibm.com wrote: > Hi Mathieu, > >> +static int do_cpu_opv(struct cpu_op *cpuop, int cpuopcnt, >> + struct cpu_opv_vaddr *vaddr_ptrs, int cpu) >> +{ >> + struct mm_struct *mm = current->mm; >> + int ret; >> + >> +retry: >> + if (cpu != raw_smp_processor_id()) { >> + ret = push_task_to_cpu(current, cpu); >> + if (ret) >> + goto check_online; >> + } >> + down_read(&mm->mmap_sem); >> + ret = vaddr_ptrs_check(vaddr_ptrs); >> + if (ret) >> + goto end; >> + preempt_disable(); >> + if (cpu != smp_processor_id()) { >> + preempt_enable(); >> + up_read(&mm->mmap_sem); >> + goto retry; >> + } > > If we have a higher priority task/s either pinned to the cpu, dont we end up > in busy-looping till the task exits/sleeps? You're right! How about we ditch the thread migration altogether, and simply perform the cpu_opv operations in a IPI handler ? This is possible now that cpu_opv uses a temporary vmap() rather than try to touch the user-space page through the current thread's page table. Thoughts ? Thanks, Mathieu > >> + ret = __do_cpu_opv(cpuop, cpuopcnt); >> + preempt_enable(); >> +end: >> + up_read(&mm->mmap_sem); >> + return ret; >> + >> +check_online: >> + /* >> + * push_task_to_cpu() returns -EINVAL if the requested cpu is not part >> + * of the current thread's cpus_allowed mask. >> + */ >> + if (ret == -EINVAL) >> + return ret; >> + get_online_cpus(); >> + if (cpu_online(cpu)) { >> + put_online_cpus(); >> + goto retry; > > + } -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com