From fe9af81e524e8a86bdd59c0cc0d9e2b0ccaf840f Mon Sep 17 00:00:00 2001 From: Pavel Tatashin Date: Thu, 19 Jul 2018 16:55:30 -0400 Subject: x86/tsc: Redefine notsc to behave as tsc=unstable Currently, the notsc kernel parameter disables the use of the TSC by sched_clock(). However, this parameter does not prevent the kernel from accessing tsc in other places. The only rationale to boot with notsc is to avoid timing discrepancies on multi-socket systems where TSC are not properly synchronized, and thus exclude TSC from being used for time keeping. But that prevents using TSC as sched_clock() as well, which is not necessary as the core sched_clock() implementation can handle non synchronized TSC based sched clocks just fine. However, there is another method to solve the above problem: booting with tsc=unstable parameter. This parameter allows sched_clock() to use TSC and just excludes it from timekeeping. So there is no real reason to keep notsc, but for compatibility reasons the parameter has to stay. Make it behave like 'tsc=unstable' instead. [ tglx: Massaged changelog ] Signed-off-by: Pavel Tatashin Signed-off-by: Thomas Gleixner Reviewed-by: Dou Liyang Reviewed-by: Thomas Gleixner Cc: steven.sistare@oracle.com Cc: daniel.m.jordan@oracle.com Cc: linux@armlinux.org.uk Cc: schwidefsky@de.ibm.com Cc: heiko.carstens@de.ibm.com Cc: john.stultz@linaro.org Cc: sboyd@codeaurora.org Cc: hpa@zytor.com Cc: peterz@infradead.org Cc: prarit@redhat.com Cc: feng.tang@intel.com Cc: pmladek@suse.com Cc: gnomes@lxorguk.ukuu.org.uk Cc: linux-s390@vger.kernel.org Cc: boris.ostrovsky@oracle.com Cc: jgross@suse.com Cc: pbonzini@redhat.com Link: https://lkml.kernel.org/r/20180719205545.16512-12-pasha.tatashin@oracle.com --- Documentation/x86/x86_64/boot-options.txt | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-) (limited to 'Documentation/x86/x86_64') diff --git a/Documentation/x86/x86_64/boot-options.txt b/Documentation/x86/x86_64/boot-options.txt index 8d109ef67ab6..66114ab4f9fe 100644 --- a/Documentation/x86/x86_64/boot-options.txt +++ b/Documentation/x86/x86_64/boot-options.txt @@ -92,9 +92,7 @@ APICs Timing notsc - Don't use the CPU time stamp counter to read the wall time. - This can be used to work around timing problems on multiprocessor systems - with not properly synchronized CPUs. + Deprecated, use tsc=unstable instead. nohpet Don't use the HPET timer. -- cgit v1.2.3