From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linutronix.de (146.0.238.70:993) by crypto-ml.lab.linutronix.de with IMAP4-SSL for ; 07 Feb 2019 17:55:59 -0000 Received: from smtp.ctxuk.citrix.com ([185.25.65.24] helo=SMTP.EU.CITRIX.COM) by Galois.linutronix.de with esmtps (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1grnu1-0000r7-D7 for speck@linutronix.de; Thu, 07 Feb 2019 18:55:58 +0100 Subject: [MODERATED] Re: [PATCH v2 0/8] PERFv2 References: <20190207132709.GA32477@hirez.programming.kicks-ass.net> <20190207143759.GP31598@tassilo.jf.intel.com> <20190207153728.GE32477@hirez.programming.kicks-ass.net> <2875fb7c-1354-c401-a7e5-6cb2cb02b40c@citrix.com> <20190207170059.GD32511@hirez.programming.kicks-ass.net> From: Andrew Cooper Message-ID: <008500cd-abc4-e09d-a808-7e38db43392e@citrix.com> Date: Thu, 7 Feb 2019 17:55:49 +0000 MIME-Version: 1.0 In-Reply-To: <20190207170059.GD32511@hirez.programming.kicks-ass.net> Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: quoted-printable Content-Language: en-GB To: speck@linutronix.de List-ID: On 07/02/2019 17:00, speck for Peter Zijlstra wrote: > On Thu, Feb 07, 2019 at 04:35:12PM +0000, speck for Andrew Cooper wrote: >> On 07/02/2019 15:37, speck for Peter Zijlstra wrote: >>> On Thu, Feb 07, 2019 at 06:37:59AM -0800, speck for Andi Kleen wrote: >>> >>>> Okay I see you rely on it being guarded by the global, but for virtual= ization >>>> support will need the copy. >>>> >>>> Would need a copy at least. >>> I've not thought abou virt yet; do we _have_ to expose the thing to >>> guests? >> Virt has been discussed at length. >> >> This feature and MSR are not architectural, and not expected to exist on >> future hardware with a silicon fix for the issue (CascadeLake B1 >> stepping and later, IIRC). >> >> By exposing the features to guests, you automatically limit their >> migrateability to a subset of the Skylake uarch processors. >> >> For Xen, I've just gone with a boot time global flag.=A0 PMU deliberately >> isn't available to guests in general, but developers wanting to do >> profiling/other can trivially flip the default. > Is that a per-guest or per-hv setting? My current patch does per-hv, but > I suppose it would not be too hard to make that per-guest. The only > question is where/how does the guest communicate this desire. This is server-wide boot time setting.=A0 I did consider per-guest, but this TSX issue isn't the only thing on my plate right now, and anyone wanting to use PMU also has to flip a different server-wide boot time setting anyway. In my otherwise copious free time, I am working on improvements to our APIs for creation, so will make it a per-guest as soon as we can sensibly express it. ~Andrew