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


  • To: Andrii Anisov <andrii_anisov@xxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxx>, <andrii.anisov@xxxxxxxxx>
  • From: George Dunlap <george.dunlap@xxxxxxxxxx>
  • Date: Tue, 11 Sep 2018 10:24:16 +0100
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  • Cc: Tim Deegan <tim@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wei.liu2@xxxxxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxx, Julien Grall <julien.grall@xxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • Delivery-date: Tue, 11 Sep 2018 09:24:28 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
  • Openpgp: preference=signencrypt

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.

The fact that we even have PRI_stime is evidence that the developer
community as a whole agrees.

>>   And then if you/we were to change this, then please
>> uniformly everywhere - there's even a second instance right in this
>> same file you change, not to speak of similar ones elsewhere

Presumably the fact that we have PRI_stime defined means that *most*
places already use this format, and the places with `:` in the middle
are outliers.  It's perfectly acceptable to change them one by one;
changing them all should only be a suggestion.

 -George

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