]> pilppa.com Git - linux-2.6-omap-h63xx.git/commit
[PATCH] RTC: Remove RTC UIP synchronization on x86
authorMatt Mackall <mpm@selenic.com>
Tue, 28 Mar 2006 09:55:58 +0000 (01:55 -0800)
committerLinus Torvalds <torvalds@g5.osdl.org>
Tue, 28 Mar 2006 17:16:00 +0000 (09:16 -0800)
commit63732c2f37093d63102d53e70866cf87bf0c0479
treebf364131da50132b6e27cfb028eee725fb4fe3e5
parent329b10bb0feacb7fb9a41389313ff0a51ae56f2a
[PATCH] RTC: Remove RTC UIP synchronization on x86

Reading the CMOS clock on x86 and some other arches currently takes up to one
second because it synchronizes with the CMOS second tick-over.  This delay
shows up at boot time as well a resume time.

This is the currently the most substantial boot time delay for machines that
are working towards instant-on capability.  Also, a quick back of the envelope
calculation (.5sec * 2M users * 1 boot a day * 10 years) suggests it has cost
Linux users in the neighborhood of a million man-hours.

An earlier thread on this topic is here:

http://groups.google.com/group/linux.kernel/browse_frm/thread/8a24255215ff6151/2aa97e66a977653d?hl=en&lr=&ie=UTF-8&rnum=1&prev=/groups%3Fhl%3Den%26lr%3D%26ie%3DUTF-8%26selm%3D1To2R-2S7-11%40gated-at.bofh.it#2aa97e66a977653d

..from which the consensus seems to be that it's no longer desirable.

In my view, there are basically four cases to consider:

1) networked, need precise walltime: use NTP
2) networked, don't need precise walltime: use NTP anyway
3) not networked, don't need sub-second precision walltime: don't care
4) not networked, need sub-second precision walltime:
   get a network or a radio time source because RTC isn't good enough anyway

So this patch series simply removes the synchronization in favor of a simple
seqlock-like approach using the seconds value.

Note that for purposes of timer accuracy on wakeup, this patch will cause us
to fire timers up to one second late.  But as the current timer resume code
will already sync once (or more!), it's no worse for short timers.

Signed-off-by: Matt Mackall <mpm@selenic.com>
Cc: Andi Kleen <ak@muc.de>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Russell King <rmk@arm.linux.org.uk>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: Kazumoto Kojima <kkojima@rr.iij4u.or.jp>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
include/asm-i386/mach-default/mach_time.h