Re: [PATCH] perfc: Print a system time in a convenient format

From: George Dunlap <george.dunlap@citrix.com>
To: Jan Beulich <JBeulich@suse.com>
Cc: Tim Deegan <tim@xen.org>,
	Stefano Stabellini <sstabellini@kernel.org>,
	Wei Liu <wei.liu2@citrix.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	George Dunlap <George.Dunlap@eu.citrix.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Ian Jackson <Ian.Jackson@eu.citrix.com>,
	andrii.anisov@gmail.com, Julien Grall <julien.grall@arm.com>,
	xen-devel <xen-devel@lists.xenproject.org>,
	"andrii_anisov@epam.com" <andrii_anisov@epam.com>
Subject: Re: [PATCH] perfc: Print a system time in a convenient format
Date: Tue, 11 Sep 2018 10:51:02 +0100	[thread overview]
Message-ID: <59c69d1a-f8ae-3cf8-3227-c89bdf116383@citrix.com> (raw)
In-Reply-To: <5B978BF202000078001E71A3@prv1-mh.provo.novell.com>

On 09/11/2018 10:33 AM, Jan Beulich wrote:
>>>> On 11.09.18 at 11:24, <george.dunlap@citrix.com> wrote:
>> On 09/11/2018 09:50 AM, Andrii Anisov wrote:
>>> Hello Jan,
>>>
>>>
>>> On 11.09.18 11:27, Jan Beulich wrote:
>>>> NAK, for two reasons: I'm not of the opinion that reading a 15 or more
>>>> digit decimal number without any separators is any easier than the
>>>> current format.
>>> It's quite subjective. IMHO timestamps measured in ns easier to
>>> understand in decimals rather than in separated 32-bit hex-es. No matter
>>> how many digital number they have.
>>> Even post processing of perfc output is easier in case of decimal
>>> timestamps. You should not parse hexes and odd separators to calculate
>>> the time elapsed between two samples.
>>
>> I agree with this.  Printing in hexadecimal is useful if you need to see
>> the bitwise structure of the content; that's of zero use when it comes
>> to timestamps.  On the contrary, you almost always want to be able to do
>> a subtraction in your head and get at least an order-of-magnitude
>> difference between the times, something which is far too difficult in hex.
> 
> I disagree - it's a matter of who looks at those numbers. Personally
> I'm quite fine doing order-of-magnitude hex math.

So quick, about how long is 0x10:00000000 ns?

Maybe you know how long that is, but I would posit that if so, you are
among a handful of people worldwide who have happened to train yourself
in that knowledge.  The millions of Xen developers and system
administrators worldwide who don't have that sense, and (like me) have
absolutely no interest in gaining that knowledge.  I have much better
things to do with my time.

Changing it to seconds (i.e., using the decimal point as a "separator")
would make sense, and I'd be in favor of a patch which did something to
that effect.  But PRI_stime is still an improvement (for the vast
majority of our users and developers); we shouldn't let the best become
the enemy of the good.

 -George

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