Commit 855615ee authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Thomas Gleixner
Browse files

x86/tsc: Remove the TSC_ADJUST clamp 



Now that all affected platforms have a microcode update; and we check
this and disable TSC_DEADLINE and print a microcode revision update
error if its too old, we can remove the TSC_ADJUST clamp.

This should help with systems where the second socket runs ahead of
the first socket and needs a negative adjustment. In this case we'd
hit the 0 clamp and give up for not achieving synchronization.

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: kevin.b.stanton@intel.com
Link: http://lkml.kernel.org/r/20170531155306.100950003@infradead.org


Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent bd9240a1

arch/x86/kernel/tsc_sync.c

+1 −20
Original line number Diff line number Diff line
@@ -71,13 +71,8 @@ static void tsc_sanitize_first_cpu(struct tsc_adjust *cur, s64 bootval, 
	 * non zero. We don't do that on non boot cpus because physical

	 * hotplug should have set the ADJUST register to a value > 0 so

	 * the TSC is in sync with the already running cpus.

	 *

	 * But we always force positive ADJUST values. Otherwise the TSC

	 * deadline timer creates an interrupt storm. We also have to

	 * prevent values > 0x7FFFFFFF as those wreckage the timer as well.

	 */

	if ((bootcpu && bootval != 0) || (!bootcpu && bootval < 0) ||

	    (bootval > 0x7FFFFFFF)) {

	if (bootcpu && bootval != 0) {

		pr_warn(FW_BUG "TSC ADJUST: CPU%u: %lld force to 0\n", cpu,

			bootval);

		wrmsrl(MSR_IA32_TSC_ADJUST, 0);
@@ -451,20 +446,6 @@ retry: 
	 */

	cur->adjusted += cur_max_warp;



	/*

	 * TSC deadline timer stops working or creates an interrupt storm

	 * with adjust values < 0 and > x07ffffff.

	 *

	 * To allow adjust values > 0x7FFFFFFF we need to disable the

	 * deadline timer and use the local APIC timer, but that requires

	 * more intrusive changes and we do not have any useful information

	 * from Intel about the underlying HW wreckage yet.

	 */

	if (cur->adjusted < 0)

		cur->adjusted = 0;

	if (cur->adjusted > 0x7FFFFFFF)

		cur->adjusted = 0x7FFFFFFF;



	pr_warn("TSC ADJUST compensate: CPU%u observed %lld warp. Adjust: %lld\n",

		cpu, cur_max_warp, cur->adjusted);

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