From: Dave Hansen <dave.hansen@linux.intel.com>
To: Borislav Petkov <bp@alien8.de>
Cc: Peter Zijlstra <peterz@infradead.org>,
linux-kernel@vger.kernel.org, tony.luck@intel.com,
tim.c.chen@linux.intel.com, hpa@linux.intel.com,
rientjes@google.com, imammedo@redhat.com, prarit@redhat.com,
toshi.kani@hp.com, brice.goglin@gmail.com, mingo@kernel.org
Subject: Re: [RFC][PATCH] x86, sched: allow topolgies where NUMA nodes share an LLC
Date: Thu, 9 Nov 2017 10:13:53 -0800 [thread overview]
Message-ID: <0b42d417-9c68-3e48-7736-db33310ba332@linux.intel.com> (raw)
In-Reply-To: <20171109140717.qmdrnbdykjsejkti@pd.tnic>
On 11/09/2017 06:07 AM, Borislav Petkov wrote:
> On Wed, Nov 08, 2017 at 04:00:38PM -0800, Dave Hansen wrote:
>> I'd argue that those two end up looking pretty much the same to an app.
>> The only difference is that the slice-local and slice-remote cache hits
>> have slightly different access latencies. I don't think it's enough to
>> notice.
>
> So if it is not enough to notice, why do we even bother? I.e., is
> there any workload showing any advantages at all from the resources
> partitioning?
If you want the *absolutely* best latency available, you turn on SNC.
You get a small boost to slice-local access and a slight penalty to
remote-slice access compared to when Sub-NUMA-Clustering is off.
You can measure this for sure, but I'll still say that most folks will
never notice. In addition, if you have access interleaved everywhere,
the "slice-local boost" and "remote-slice penalty" roughly cancel
each-other out.
prev parent reply other threads:[~2017-11-09 18:14 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-06 22:15 Dave Hansen
2017-11-07 8:30 ` Peter Zijlstra
2017-11-07 16:22 ` Dave Hansen
2017-11-07 19:56 ` Borislav Petkov
2017-11-08 9:31 ` Peter Zijlstra
2017-11-09 0:00 ` Dave Hansen
2017-11-09 14:07 ` Borislav Petkov
2017-11-09 18:13 ` Dave Hansen [this message]
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