From: Peter Zijlstra <peterz@infradead.org>
To: "Luck, Tony" <tony.luck@intel.com>
Cc: "Schofield, Alison" <alison.schofield@intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@kernel.org>, Borislav Petkov <bp@alien8.de>,
"x86@kernel.org" <x86@kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Dave Hansen <dave.hansen@linux.intel.com>,
Tim Chen <tim.c.chen@linux.intel.com>,
"H. Peter Anvin" <hpa@linux.intel.com>,
David Rientjes <rientjes@google.com>,
Igor Mammedov <imammedo@redhat.com>,
Prarit Bhargava <prarit@redhat.com>,
"brice.goglin@gmail.com" <brice.goglin@gmail.com>
Subject: Re: [PATCH] x86, sched: Allow NUMA nodes to share an LLC on Intel platforms
Date: Wed, 10 Feb 2021 09:10:35 +0100 [thread overview]
Message-ID: <YCOU+1GT4+hxqH5/@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <af770863e70340d294c324fd7004f658@intel.com>
On Tue, Feb 09, 2021 at 11:09:27PM +0000, Luck, Tony wrote:
> > +#define X86_BUG_NUMA_SHARES_LLC X86_BUG(25) /* CPU may enumerate an LLC shared by multiple NUMA nodes */
>
> During internal review I wondered why this is a "BUG" rather than a "FEATURE" bit.
>
> Apparently, the suggestion for "BUG" came from earlier community discussions.
>
> Historically it may have seemed reasonable to say that a cache cannot span
> NUMA domains. But with more and more things moving off the motherboard
> and into the socket, this doesn't seem too weird now.
If you look at the details this SNC LLC span doesn't behave quite right
either.
It really isn't a regular cache, but behaves a bit like a mash-up of the
s390 book caches and a normal LLC.
Did anybody play with adding the book domain to these SNC
configurations? Can we detect SNC other than by this quirk?
next prev parent reply other threads:[~2021-02-10 8:12 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-09 22:39 [PATCH] x86, sched: Allow NUMA nodes to share an LLC on Intel platforms Alison Schofield
2021-02-09 23:09 ` Luck, Tony
2021-02-10 8:10 ` Peter Zijlstra [this message]
2021-02-10 17:41 ` Dave Hansen
2021-02-10 8:05 ` Peter Zijlstra
2021-02-10 15:22 ` Dave Hansen
2021-02-10 19:38 ` Peter Zijlstra
2021-02-10 22:11 ` Alison Schofield
2021-02-16 11:29 ` Peter Zijlstra
2021-02-16 19:53 ` Alison Schofield
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