Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753554AbeAHRZ0 convert rfc822-to-8bit (ORCPT + 1 other); Mon, 8 Jan 2018 12:25:26 -0500 Received: from smtp-out4.electric.net ([192.162.216.181]:64848 "EHLO smtp-out4.electric.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752828AbeAHRZX (ORCPT ); Mon, 8 Jan 2018 12:25:23 -0500 From: David Laight To: 'Willy Tarreau' , "linux-kernel@vger.kernel.org" , "stable@vger.kernel.org" Subject: RE: Feedback on 4.9 performance after PTI fixes Thread-Topic: Feedback on 4.9 performance after PTI fixes Thread-Index: AQHTh6EYf/1x71Ird0WcWm7w/wxm5aNqOycQ Date: Mon, 8 Jan 2018 17:26:06 +0000 Message-ID: References: <20180107101856.GA9590@1wt.eu> In-Reply-To: <20180107101856.GA9590@1wt.eu> Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.33] Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 X-Outbound-IP: 156.67.243.126 X-Env-From: David.Laight@ACULAB.COM X-Proto: esmtps X-Revdns: X-HELO: AcuMS.aculab.com X-TLS: TLSv1.2:ECDHE-RSA-AES256-SHA384:256 X-Authenticated_ID: X-PolicySMART: 3396946, 3397078 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: From: Willy Tarreau > Sent: 07 January 2018 10:19 ... > The impact inside VMs is quite big but it's not where we usuall install > processes sensitive to syscall performance. I could find an even higher > impact on a packet generation program dropping from 2.5 Mpps to 600kpps > in the VM after the fix, but it doesn't make much sense to do this in > VMs so I don't really care. Why not? It will be related to the cost of sending (and probably receiving) network traffic in a VM. This is something that is done a lot. Maybe not packet generation, but a UDP/IP benchmark inside a VM would be sensible. It may well be that moderate ethernet packet rates cause a massive performance drop when the host kernel has PTI enabled. David