[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <51C48ADD.207@sgi.com>
Date: Fri, 21 Jun 2013 12:18:21 -0500
From: Nathan Zimmer <nzimmer@....com>
To: "H. Peter Anvin" <hpa@...or.com>
CC: Greg KH <gregkh@...uxfoundation.org>, <holt@....com>,
<travis@....com>, <rob@...dley.net>, <tglx@...utronix.de>,
<mingo@...hat.com>, <yinghai@...nel.org>,
<akpm@...ux-foundation.org>, <x86@...nel.org>,
<linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [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
--
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/
Powered by blists - more mailing lists