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| author | Andy Lutomirski <luto@kernel.org> | 2018-10-05 00:44:45 +0300 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2018-10-05 11:12:18 +0300 |
| commit | bcc4a62a73cb65327d7268fbfa3a786d603f52dc (patch) | |
| tree | c2e94ba24842651f81782fb22a51df0382d5e2b5 | |
| parent | 89fe0a1f1c694a3b0b3cfa8c0952d603753f36df (diff) | |
| download | linux-bcc4a62a73cb65327d7268fbfa3a786d603f52dc.tar.xz | |
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 <luto@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/f66f53d81150bbad47d7b282c9207a71a3ce1c16.1538689401.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
| -rw-r--r-- | arch/x86/include/asm/vgtod.h | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/arch/x86/include/asm/vgtod.h b/arch/x86/include/asm/vgtod.h index d17b092b9f1b..69d05c6d47f5 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; |