From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AH8x226wIiwVUW3M1aq+h/C1AToacTwUG1DvJbMujY/59njjh3kAUHk2+xCqfof4Ea9Vh2sC7Eow ARC-Seal: i=1; a=rsa-sha256; t=1516888272; cv=none; d=google.com; s=arc-20160816; b=NlIqMYAyD4qb+rqFytXdV/Y8SABDixmXCyJ09UkgPXmFBRYaSdQxK7bUlXMKGX+46R MuIBEuAkqyGYo+mWPIKiC952Ig08fDQ77JrLYSMUgmMxASGsVW5oZW6xNmwidN4pZ6Nf kuTtI1KOgIRsLYeKXRh6yWyaAPuHmuTI/eJOEL3wMiD5jwtue4uJjNIsNRIgk8s7nQci vWXG/JrpisuMXf7YYnGIAh9Db9Tds6i6BUjMRD1NKyhLyqU9xsMglIVP1St0z66mQMV6 HClf+mZVBZ3UVdFMSezJ3uIqplbvqhLXKvz/7DxpmyCtcdQH3atJO5V2hujRTjk7BWTI xpng== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=user-agent:in-reply-to:content-disposition:mime-version:references :message-id:subject:cc:to:from:date:dkim-signature :arc-authentication-results; bh=sRlkPNByH0zlfO5XRgP51eLWpr0TrZl61S3VM6mavYk=; b=FSlTXDNoBUTuDTA5VjKq9fHP1yuPx9eyIygB15n8eOpyh7Er72xYsxEiBWOFqyGmSO 0Z65CmLcA27yF31akkWL7zkwY1jPW/x21O8p4us86vFXPkHXBZyWwvt3/LYKUSUMeuVC cDo+ReMTuhmgohCMtMyT1jbg/5F8JSiqaVDKDFXanLG4APl5REXzZt2Ey60EIvf6dbyI mJG9lldDA8MsJrN08MXamiVSL7mOAr1UByD9qIW4zpGyjf9dyvDJOpDs942ejWSTvII8 6Bx6bpoSddokn5c859J+A4WGuRvtjaEgkeStZmO/MP/A5IAs0Yd7vq/kNqcj5W7w0Ber 4GJQ== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@infradead.org header.s=merlin.20170209 header.b=lrvI56WS; spf=pass (google.com: best guess record for domain of peterz@infradead.org designates 205.233.59.134 as permitted sender) smtp.mailfrom=peterz@infradead.org Authentication-Results: mx.google.com; dkim=pass header.i=@infradead.org header.s=merlin.20170209 header.b=lrvI56WS; spf=pass (google.com: best guess record for domain of peterz@infradead.org designates 205.233.59.134 as permitted sender) smtp.mailfrom=peterz@infradead.org Date: Thu, 25 Jan 2018 14:50:55 +0100 From: Peter Zijlstra To: Arjan van de Ven Cc: Tim Chen , linux-kernel@vger.kernel.org, KarimAllah Ahmed , Andi Kleen , Andrea Arcangeli , Andy Lutomirski , Ashok Raj , Asit Mallick , Borislav Petkov , Dan Williams , Dave Hansen , David Woodhouse , Greg Kroah-Hartman , "H . Peter Anvin" , Ingo Molnar , Janakarajan Natarajan , Joerg Roedel , Jun Nakajima , Laura Abbott , Linus Torvalds , Masami Hiramatsu , Paolo Bonzini , rkrcmar@redhat.com, Thomas Gleixner , Tom Lendacky , x86@kernel.org Subject: Re: [RFC PATCH 1/2] x86/ibpb: Skip IBPB when we switch back to same user process Message-ID: <20180125135055.GK2249@hirez.programming.kicks-ass.net> References: <20180125085820.GV2228@hirez.programming.kicks-ass.net> <20180125092233.GE2295@hirez.programming.kicks-ass.net> <86541aca-8de7-163d-b620-083dddf29184@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <86541aca-8de7-163d-b620-083dddf29184@linux.intel.com> User-Agent: Mutt/1.9.2 (2017-12-15) X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1590523944221221739?= X-GMAIL-MSGID: =?utf-8?q?1590572637562872543?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On Thu, Jan 25, 2018 at 05:21:30AM -0800, Arjan van de Ven wrote: > > > > This means that 'A -> idle -> A' should never pass through switch_mm to > > begin with. > > > > Please clarify how you think it does. > > > > the idle code does leave_mm() to avoid having to IPI CPUs in deep sleep states > for a tlb flush. The intel_idle code does, not the idle code. This is squirreled away in some driver :/ > (trust me, that you really want, sequentially IPI's a pile of cores in a deep sleep > state to just flush a tlb that's empty, the performance of that is horrific) Hurmph. I'd rather fix that some other way than leave_mm(), this is piling special on special.