lkml.org 
[lkml]   [2013]   [Jun]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [RFC 0/2] Delay initializing of large sections of memory
On 06/21/2013 12:03 PM, H. Peter Anvin wrote:
> On 06/21/2013 09:51 AM, Greg KH wrote:
>> On Fri, Jun 21, 2013 at 11:25:32AM -0500, Nathan Zimmer wrote:
>>> This rfc patch set delays initializing large sections of memory until we have
>>> started cpus. This has the effect of reducing startup times on large memory
>>> systems. On 16TB it can take over an hour to boot and most of that time
>>> is spent initializing memory.
>>>
>>> We avoid that bottleneck by delaying initialization until after we have
>>> started multiple cpus and can initialize in a multithreaded manner.
>>> This allows us to actually reduce boot time rather then just moving around
>>> the point of initialization.
>>>
>>> Mike and I have worked on this set for a while, with him doing the most of the
>>> heavy lifting, and are eager for some feedback.
>> Why make this a config option at all, why not just always do this if the
>> memory size is larger than some specific number (like 8TB?)
>>
>> Otherwise the distros will always enable this option, and having it be a
>> configuration choice doesn't make any sense.
>>
> Since you made it a compile time option, it would be good to know how
> much code it adds, but otherwise I agree with Greg here... this really
> shouldn't need to be an option. It *especially* shouldn't need to be a
> hand-set runtime option (which looks quite complex, to boot.)
The patchset as a whole is just over 400 lines so it doesn't add alot.
If I were to pull the .config option it would probably remove 30 lines.

The command line option is too complex but some of the data I haven't
found a way
to get at runtime yet.


>
> I suspect the cutoff for this should be a lot lower than 8 TB even, more
> like 128 GB or so. The only concern is to not set the cutoff so low
> that we can end up running out of memory or with suboptimal NUMA
> placement just because of this.
Even at lower amounts of ram there is an positive impact.I it knocks
time off
boot even at as small as a 1TB of ram.

> Also, in case it is not bloody obvious: whatever memory the kernel image
> was loaded into MUST be considered "online", even if it is loaded way high.
>
> -hpa
>
>
>
>


Ok


\
 
 \ /
  Last update: 2013-06-21 19:41    [W:0.172 / U:3.376 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site