lkml.org 
[lkml]   [2015]   [Oct]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [v3, 3/3] MIPS: VDSO: Add implementations of gettimeofday() and clock_gettime()
On 10/27/2015 02:02 PM, David Daney wrote:
> On 10/27/2015 01:46 PM, Leonid Yegoshin wrote:
> [...]
>>
>> And finally. clock scaling - what we would do if there are two CPUs with
>> different clock ratios in system? It seems like common kernel timing
>> subsystem can handle that.
>>
>
> The code that executes in userspace must have access to a consistent
> clock source. If you are running on a SMP system that doesn't have
> synchronized CP0.Count registers, then your gettimeofday() cannot use
> CP0.Count (RDHWR $2).

Right, I agree.

>
> As far as I know, CP0.Count is the only available counter visible to
> userspace, so you would have to disable the accelerated versions of
> gettimeofday() where you cannot assert that the counters are always
> synchronized.

Any system with GIC may have access to the same GIC global counter in a
special separate page available for mapping by user in RO mode and it
seems Alex did that.

Besides that this GIC global counter is used as a major system
clocksource in systems with GIC.

- Leonid




\
 
 \ /
  Last update: 2015-10-27 22:41    [W:0.053 / U:0.052 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site