From bcc4a62a73cb65327d7268fbfa3a786d603f52dc Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Thu, 4 Oct 2018 14:44:45 -0700 Subject: x86/vdso: Document vgtod_ts better After reading do_hres() and do_course() and scratching my head a bit, I figured out why the arithmetic is strange. Document it. Signed-off-by: Andy Lutomirski Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/f66f53d81150bbad47d7b282c9207a71a3ce1c16.1538689401.git.luto@kernel.org Signed-off-by: Ingo Molnar --- arch/x86/include/asm/vgtod.h | 9 +++++++++ 1 file changed, 9 insertions(+) (limited to 'arch/x86/include/asm/vgtod.h') diff --git a/arch/x86/include/asm/vgtod.h b/arch/x86/include/asm/vgtod.h index d17b092b9f1bc..69d05c6d47f58 100644 --- a/arch/x86/include/asm/vgtod.h +++ b/arch/x86/include/asm/vgtod.h @@ -13,6 +13,15 @@ typedef u64 gtod_long_t; typedef unsigned long gtod_long_t; #endif +/* + * There is one of these objects in the vvar page for each + * vDSO-accelerated clockid. For high-resolution clocks, this encodes + * the time corresponding to vsyscall_gtod_data.cycle_last. For coarse + * clocks, this encodes the actual time. + * + * To confuse the reader, for high-resolution clocks, nsec is left-shifted + * by vsyscall_gtod_data.shift. + */ struct vgtod_ts { u64 sec; u64 nsec; -- cgit v1.2.3