From: Dave Hansen <dave.hansen@intel.com>
To: Zhang Rui <rui.zhang@intel.com>, Feng Tang <feng.tang@intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
"H . Peter Anvin" <hpa@zytor.com>,
Peter Zijlstra <peterz@infradead.org>,
x86@kernel.org, linux-kernel@vger.kernel.org
Cc: tim.c.chen@intel.com, Xiongfeng Wang <wangxiongfeng2@huawei.com>,
liaoyu15@huawei.com
Subject: Re: [PATCH v1 1/2] x86/tsc: use logical_package as a better estimation of socket numbers
Date: Mon, 24 Oct 2022 08:42:30 -0700 [thread overview]
Message-ID: <dfd2fb43-2a19-545a-fea8-f793a685ef30@intel.com> (raw)
In-Reply-To: <6636557f617ea5a1a1ab6f30f7aea0ececdd2a36.camel@intel.com>
On 10/22/22 09:12, Zhang Rui wrote:
>>> I'm not sure if we have a perfect solution here.
>> Are the implementations fixable?
> currently, I don't have any idea.
>
>> Or, at least tolerable?
That would be great to figure out before we start throwing more patches
around.
>> For instance, I can live with the implementation being a bit goofy
>> when
>> kernel commandlines are in play. We can pr_info() about those cases.
> My understanding is that the cpus in the last package may still have
> small cpu id value. This means that the 'logical_packages' is hard to
> break unless we boot with very small CPU count and happened to disable
> all cpus in one/more packages. Feng is experiencing with this and may
> have some update later.
>
> If this is the case, is this a valid case that we need to take care of?
Well, let's talk through it a bit.
What is the triggering event and what's the fallout?
Is the user on a truly TSC stable system or not?
What kind of maxcpus= argument do they need to specify? Is it something
that's likely to get used in production or is it most likely just for
debugging?
What is the maxcpus= fallout? Does it over estimate or under estimate
the number of logical packages?
How many cases outside of maxcpus= do we know of that lead to an
imprecise "logical packages" calculation?
Does this lead to the TSC being mistakenly marked stable when it is not,
or *not* being marked stable when it is?
Let's get all of that info in one place and make sure we are all agreed
on the *problem* before we got to the solution space.
next prev parent reply other threads:[~2022-10-24 17:09 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-21 6:21 [PATCH v1 1/2] x86/tsc: use logical_package as a better estimation of socket numbers Feng Tang
2022-10-21 6:21 ` [PATCH v1 2/2] x86/tsc: Extend watchdog check exemption to 4-Sockets platform Feng Tang
2023-06-02 18:00 ` Paul E. McKenney
2023-06-05 6:28 ` Feng Tang
2022-10-21 15:00 ` [PATCH v1 1/2] x86/tsc: use logical_package as a better estimation of socket numbers Zhang Rui
2022-10-21 16:21 ` Dave Hansen
2022-10-22 16:12 ` Zhang Rui
2022-10-24 15:42 ` Dave Hansen [this message]
2022-10-25 7:35 ` Feng Tang
2022-10-24 7:37 ` Feng Tang
2022-10-24 15:43 ` Dave Hansen
2022-10-25 7:57 ` Feng Tang
2022-11-04 7:21 ` Feng Tang
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