linux-kernel - Re: [PATCHES/RFC] Re: A concern about overflow ring buffer mode

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Message-Id: <20181029.104827.680192866924184016.davem@davemloft.net>
Date:   Mon, 29 Oct 2018 10:48:27 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     kan.liang@...ux.intel.com
Cc:     acme@...nel.org, linux-kernel@...r.kernel.org, wangnan0@...wei.com,
        jolsa@...nel.org, namhyung@...nel.org, kan.liang@...el.com,
        ak@...ux.intel.com, yao.jin@...ux.intel.com, peterz@...radead.org
Subject: Re: [PATCHES/RFC] Re: A concern about overflow ring buffer mode

From: "Liang, Kan" <kan.liang@...ux.intel.com>
Date: Mon, 29 Oct 2018 13:42:56 -0400

> 
> 
> On 10/29/2018 1:40 PM, David Miller wrote:
>> From: "Liang, Kan" <kan.liang@...ux.intel.com>
>> Date: Mon, 29 Oct 2018 10:33:06 -0400
>> 
>>> I just realized that the problem in KNL will be back if we switch
>>> back to non-overwrite mode.
>> What is KNL?
>>
> Intel Xeon Phi Processor, Knights Landing.

I don't understand how a specific piece of hardware directly leads to
ring buffer processing timeouts, or multi-minute thread map processing
times...

You'll have to explain all of the details of your test scenerio, and
the exact problems triggers, which caused you to write these patches
which causes serious regressions for what I consider a core simple use
case of perf top.

And that's running perf top during a parallel kernel build.