From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ie0-f173.google.com (mail-ie0-f173.google.com [209.85.223.173]) by kanga.kvack.org (Postfix) with ESMTP id F07E96B0032 for ; Tue, 28 Apr 2015 18:56:29 -0400 (EDT) Received: by iecrt8 with SMTP id rt8so30425637iec.0 for ; Tue, 28 Apr 2015 15:56:29 -0700 (PDT) Received: from mail-ie0-x22e.google.com (mail-ie0-x22e.google.com. [2607:f8b0:4001:c03::22e]) by mx.google.com with ESMTPS id f19si19971336icl.8.2015.04.28.15.56.29 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 28 Apr 2015 15:56:29 -0700 (PDT) Received: by iebrs15 with SMTP id rs15so30408775ieb.3 for ; Tue, 28 Apr 2015 15:56:29 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20150428221553.GA5770@node.dhcp.inet.fi> References: <20150428221553.GA5770@node.dhcp.inet.fi> Date: Tue, 28 Apr 2015 15:56:29 -0700 Message-ID: Subject: Re: PCID and TLB flushes (was: [GIT PULL] kdbus for 4.1-rc1) From: Linus Torvalds Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: "Kirill A. Shutemov" Cc: Andy Lutomirski , Dave Hansen , Andrew Morton , Mel Gorman , Rik van Riel , Linux Kernel Mailing List , linux-mm , the arch/x86 maintainers On Tue, Apr 28, 2015 at 3:15 PM, Kirill A. Shutemov wrote: > > I talked with Dave about implementing PCID and he thinks that it will be > net loss. So I'm told that Suresh Siddha actually had a patch inside Intel to use PCID (back when he worked for Intel, I think he left), and that it was a wash in their testing. I never saw the patch, and it might be interesting to try it again, but there is some reason to believe that it doesn't make much of a difference. Unlike most of the traditional RISC machines that got big speedups, Intel TLB walking is so good that it likely isn't nearly as noticeable, and it likely *does* result in more IPI's etc. Possibly not a lot more, but if the win isn't big... So I don't want to discourage you, because I'd love to see what the patch looks like and if we can find cases where it matters, but I do want to set expectations right. It's unlikely to be a big issue. Linus -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org