Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752406AbdFVFTy (ORCPT ); Thu, 22 Jun 2017 01:19:54 -0400 Received: from mail.kernel.org ([198.145.29.99]:41904 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751064AbdFVFTx (ORCPT ); Thu, 22 Jun 2017 01:19:53 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 74E7822B6A Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=luto@kernel.org MIME-Version: 1.0 In-Reply-To: References: From: Andy Lutomirski Date: Wed, 21 Jun 2017 22:19:30 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v3 00/11] PCID and improved laziness To: Linus Torvalds Cc: Andy Lutomirski , "the arch/x86 maintainers" , Linux Kernel Mailing List , Borislav Petkov , Andrew Morton , Mel Gorman , "linux-mm@kvack.org" , Nadav Amit , Rik van Riel , Dave Hansen , Arjan van de Ven , Peter Zijlstra Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 925 Lines: 25 On Wed, Jun 21, 2017 at 11:23 AM, Linus Torvalds wrote: > On Tue, Jun 20, 2017 at 10:22 PM, Andy Lutomirski wrote: >> There are three performance benefits here: > > Side note: can you post the actual performance numbers, even if only > from some silly test program on just one platform? Things like lmbench > pipe benchmark or something? > > Or maybe you did, and I just missed it. But when talking about > performance, I'd really like to always see some actual numbers. Here are some timings using KVM: pingpong between two processes using eventfd: patched: 883ns unpatched: 1046ns (with considerably higher variance) madvise(MADV_DONTNEED); write to the page; switch CPUs: patched: ~12.5us unpatched: 19us The latter test is a somewhat contrived example to show off the improved laziness. Current kernels send an IPI on each iteration if the system is otherwise idle.