From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752063AbdGER7x (ORCPT ); Wed, 5 Jul 2017 13:59:53 -0400 Received: from mail-it0-f66.google.com ([209.85.214.66]:33021 "EHLO mail-it0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751716AbdGER7w (ORCPT ); Wed, 5 Jul 2017 13:59:52 -0400 MIME-Version: 1.0 In-Reply-To: References: <1498503368-20173-1-git-send-email-vikas.shivappa@linux.intel.com> <1498503368-20173-9-git-send-email-vikas.shivappa@linux.intel.com> From: Tony Luck Date: Wed, 5 Jul 2017 10:59:50 -0700 Message-ID: Subject: Re: [PATCH 08/21] x86/intel_rdt/cqm: Add RMID(Resource monitoring ID) management To: Thomas Gleixner Cc: Vikas Shivappa , X86-ML , Linux Kernel Mailing List , "H. Peter Anvin" , Peter Zijlstra , ravi.v.shankar@intel.com, vikas.shivappa@intel.com, "Yu, Fenghua" , andi.kleen@intel.com Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > In case that a RMID was never used on a particular package, the state check > forces an IPI on all packages unconditionally. That's suboptimal at least. > > We know on which package a given RMID was used, so we could restrict the > checks to exactly these packages, but I'm not sure it's worth the > trouble. We might at least document that and explain why this is > implemented in that way. We only allocate RMIDs when a user makes a directory. I don't think we should consider options that slow down context switch in order to keep track of which packages were used just to make mkdir(2) a bit faster in the case where we need to check the limbo list. We could make the check of the limbo list less costly by using a bitmask to keep track of which packages have already found that the llc_occupancy is below the threshold. But I'd question whether the extra complexity in the code was really worth it. -Tony [on vacation - responses will be slow]