linux-kernel - Re: [RFC patch 0/4] TSC calibration improvements

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Date:	Sat, 6 Sep 2008 14:15:00 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Thomas Gleixner <tglx@...utronix.de>
cc:	Alok Kataria <akataria@...are.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	LKML <linux-kernel@...r.kernel.org>,
	Arjan van de Veen <arjan@...radead.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Dan Hecht <dhecht@...are.com>,
	Garrett Smith <garrett@...are.com>
Subject: Re: [RFC patch 0/4] TSC calibration improvements



On Sat, 6 Sep 2008, Thomas Gleixner wrote:
> > 
> > Show some _taste_.
> 
> Tell the hardware dudes who made that crap so difficult

No. I'm telling you, because that patch IS CRAP.

> Over which _whole_ thing ? You want to have the very very fast thing,
> which is not reliable under all circumstances as Alok pointed out and
> I merily added a sanity check around that for testing.

You can move that thing _out_ into a function of its own.

Look at this piece fo CRAP, and tell me, HOW MANY TIMES do you want to 
repeat it?

+               /*
+                * Return the fast_calibrate value when neither hpet
+                * nor pmtimer are available.
+                */
+               if (!hpet && !ref1 && !ref2) {
+                       printk("Fast TSC calibration using PIT\n");
+                       return fast_calibrate;
+               }
+
+               /* Check, whether the sampling was disturbed by an SMI */
+               if (tsc1 == ULLONG_MAX || tsc2 == ULLONG_MAX)
+                       goto slowpath;
+
+               tsc2 = (tsc2 - tsc1) * 1000000LL;
+               if (hpet)
+                       tsc2 = calc_hpet_ref(tsc2, ref1, ref2);
+               else
+                       tsc2 = calc_pmtimer_ref(tsc2, ref1, ref2);
+
+               /* Check the reference deviation */
+               delta = ((u64) fast_calibrate) * 100;
+               do_div(delta, tsc2);
+
+               if (delta >= 90 && delta <= 110) {
+                       printk("Fast TSC calibration using PIT\n");
+                       return fast_calibrate;
+               }
+       }

Here's a hint: we don't do cut-and-paste programming. And we don't get 
extra points for bloating a single function with the same unreadable code 
over and over and over again. 

How many copies do you want? And here's a hint: the answer is _one_. If 
you get any other answer, your patch is SHIT.

			Linus
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