linux-kernel - Re: RTC subsystem and fractions of seconds

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [day] [month] [year] [list]

Date:	Sun, 7 Jan 2007 23:31:19 +0100
From:	Philippe De Muyter <phdm@...qel.be>
To:	hugh@...itas.com, david-b@...bell.net
Cc:	linux-kernel@...r.kernel.org
Subject: Re: RTC subsystem and fractions of seconds


On Sun, 7 Jan 2007, Hugh Dickins wrote:
> Author: Matt Mackall <mpm@...enic.com>
> 
>     [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.

That is true if kernel's idea of an RTC's precision is 1 second.  With better
RTC's (e.g. m41t81) this delay can be reduced to 0.01 second, which is
acceptable IMHO in the boot phase.  That needs however changes in the kernel
interface to RTC's :

    - read_time should take a new parameter *nsec (or struct rtc_time should
    contain a new nsec field, so that the RTC can report its complete time
    information to the kernel.

    - struct rtc_device (or rtc_class_ops with another name) should contain
    a new field giving the RTC's resolution in nsecs, if we want to avoid the
    loop, but do not want our 0.01 second precision be destructed by always
    adding 0.5 second in rtc_hctosys
    
Philippe
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/