Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933665Ab2EWPEz (ORCPT ); Wed, 23 May 2012 11:04:55 -0400 Received: from nat28.tlf.novell.com ([130.57.49.28]:37949 "EHLO nat28.tlf.novell.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932533Ab2EWPEx convert rfc822-to-8bit (ORCPT ); Wed, 23 May 2012 11:04:53 -0400 Message-Id: <4FBD18D20200007800085951@nat28.tlf.novell.com> X-Mailer: Novell GroupWise Internet Agent 12.0.0 Date: Wed, 23 May 2012 16:05:22 +0100 From: "Jan Beulich" To: "Alex Shi" Cc: , , , , , , , , , , , , , , , , , , , , , , , , , , , , Subject: Re: [PATCH v7 8/8] x86/tlb: just do tlb flush on one of siblings of SMT References: <1337782555-8088-1-git-send-email-alex.shi@intel.com> <1337782555-8088-9-git-send-email-alex.shi@intel.com> In-Reply-To: <1337782555-8088-9-git-send-email-alex.shi@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 8BIT Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1250 Lines: 36 >>> On 23.05.12 at 16:15, Alex Shi wrote: > + /* doing flush on both siblings of SMT is just wasting time */ > + cpumask_copy(&flush_mask, cpumask); > + if (likely(smp_num_siblings > 1)) { > + rand = jiffies; > + /* See "Numerical Recipes in C", second edition, p. 284 */ > + rand = rand * 1664525L + 1013904223L; > + rand &= 0x1; > + > + for_each_cpu(cpu, &flush_mask) { > + sblmask = cpu_sibling_mask(cpu); > + if (cpumask_subset(sblmask, &flush_mask)) { > + if (rand == 0) > + cpu_clear(cpu, flush_mask); > + else > + cpu_clear(cpumask_next(cpu, sblmask), > + flush_mask); > + } > + } > + } > + There is no comment or anything else indicating that this is suitable for dual-thread CPUs only - when there are more than 2 threads per core, the intended effect won't be achieved. I'd recommend making the logic generic from the beginning, but if that doesn't seem feasible to you, at least a comment stating the limitation should be added imo. Jan -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/