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Message-ID: <74a372a8-6908-4f9f-a79d-febeb6136379@amd.com> Date: Wed, 25 Oct 2023 11:01:22 -0500 From: "Moger, Babu" <babu.moger@....com> To: "Luck, Tony" <tony.luck@...el.com>, "Moger, Babu" <bmoger@....com>, "Yu, Fenghua" <fenghua.yu@...el.com>, "Chatre, Reinette" <reinette.chatre@...el.com>, Peter Newman <peternewman@...gle.com>, Jonathan Corbet <corbet@....net>, Shuah Khan <skhan@...uxfoundation.org>, "x86@...nel.org" <x86@...nel.org> Cc: Shaopeng Tan <tan.shaopeng@...itsu.com>, James Morse <james.morse@....com>, Jamie Iles <quic_jiles@...cinc.com>, Randy Dunlap <rdunlap@...radead.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>, "patches@...ts.linux.dev" <patches@...ts.linux.dev> Subject: Re: [PATCH] x86/resctrl: mba_MBps: Fall back to total b/w if local b/w unavailable Hi Tony, On 10/24/23 18:43, Luck, Tony wrote: >> Is this customer requirement ? > > Any customer using the mba_MBps feedback mount option will need this > on platforms that don't support local bandwidth measurement. > >> What do you mean by " If local bandwidth measurement is not available" ? >> Is the hardware supports only total bandwidth and not local? > > There's going to be an Intel CPU that will only provide "total" bandwidth. ok. Why dont you use get_mbm_state which is already available instead of writing another function(get_mbm_data). You can pass evtid, rmid, domain information. Decide the evtid based on what is available. I think that will make code simpler. > > The CPUID enumeration in (CPUID.(EAX=0FH, ECX=1H) ).EDX{2} > will be "0" indicating that the local mbm monitor event is not supported. > >> It can get real ugly if we try to handle one special case. > > Hard to predict the future (I didn't see this coming, or I'd have had Vikas > implement the fallback in the original mba_MBps code). But I don't believe > this will be a one-off special case. > > I'm also wondering why this feedback loop picked "local" rather than "total". > I dug into the e-mail archives, and I don't see any discussion. There's just > an RFC series, and then the v2 series was applied with a few small suggestions > from Thomas to make things cleaner.. May be MSR write which feedback loop does only has local effect. This will be interesting to know. -- Thanks Babu Moger
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