x86: fix more TSC clock source calibration errors (8c660065) · Commits · 戴 / test

The previous patch wasn't correctly handling the 'count' variable. If a CPU gave bad results on the 1st or 2nd run but good results on the 3rd, it wouldn't do the correct thing. No idea if any such CPU exists, but the patch below handles that case by discarding the bad runs. If a bad result (too quick, or too slow) occurs on any of the 3 runs it will be discarded. Also updated some comments to explain what's going on. Signed-off-by:

Dave Johnson <djohnson@sw.starentnetworks.com> Signed-off-by:

Ingo Molnar <mingo@elte.hu> Signed-off-by:

Thomas Gleixner <tglx@linutronix.de>

arch/x86/kernel/tsc_32.c

+20 −14

Original line number	Diff line number	Diff line
		@@ -137,14 +137,13 @@ unsigned long native_calculate_cpu_khz(void)

		local_irq_save(flags);

		/* run 3 times to ensure the cache is warm */
		/* run 3 times to ensure the cache is warm and to get an accurate reading */
		for (i = 0; i < 3; i++) {
		mach_prepare_counter();
		rdtscll(start);
		mach_countup(&count);
		rdtscll(end);
		delta64 = min(delta64, (end - start));
		}

		/*
		* Error: ECTCNEVERSET
		* The CTC wasn't reliable: we got a hit on the very first read,
		@@ -152,14 +151,21 @@ unsigned long native_calculate_cpu_khz(void)
		* 32 bits..
		*/
		if (count <= 1)
		goto err;

		/* cpu freq too fast: */
		if (delta64 > (1ULL<<32))
		goto err;
		continue;

		/* cpu freq too slow: */
		if (delta64 <= CALIBRATE_TIME_MSEC)
		if ((end - start) <= CALIBRATE_TIME_MSEC)
		continue;

		/*
		* We want the minimum time of all runs in case one of them
		* is inaccurate due to SMI or other delay
		*/
		delta64 = min(delta64, (end - start));
		}

		/* cpu freq too fast (or every run was bad): */
		if (delta64 > (1ULL<<32))
		goto err;

		delta64 += CALIBRATE_TIME_MSEC/2; /* round for do_div */

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